MORPHOLOGY AND MORPHOMETRY OF THE LYMPH NODES OF THE DROMEDARY (Camelus dromedarius)

By Lemiaa Eissa Saeed B.V.Sc., 1996

A thesis submitted in partial fulfillment of the

requirements for the degree of Master of Veterinary

Science

(M.V.Sc.)

Supervisor: Professor Dafalla Ibrahim Osman

Department of Anatomy

Faculty of Veterinary Medicine

University of Khartoum

January 2004

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DEDICATION

To my Father, Eissa and Mother, Mona. To my Aunt, Ihsan. To late Grandfather , Abdel-Rahman With love

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ACKNOWLEDGEMENTS

First praise is to Almighty ALLA for giving me health and strength to carry out this work. I wish to express my deepest thanks, gratitude and indebtedness to my supervisor Professor Daffalla Ibrahim, for his supervision, guidance, suggestion and careful scrutiny in all aspects of this study.

Sincere thanks are due to Dr. Ali Bashir Abdalla, Head of the Department of Anatomy for his advice and help during the course of this study. Special thanks to Mr. Alsadig Ismail for his help on the morphometric investigation.

Deepest gratitude is expressed to Mr. Mahjoup Jaafar, Mr. Elamin Elsufi, Mr. Mohamed Zein El-Sharif, Mr. Zakaria saleh, Mr. Adel Faroug, Mr. Mortada Mahgoup, Mr. Ali Bashir and Miss Sara Abo-Algasim for their assistance during the period of my work. My thanks are also extended to the rest of the staff members of the Department of Anatomy, Faculty of Veterinary Medicine, University of Khartoum. I am also grateful to Mr. Seyed Yosif, Ahmed Defalla and Ali Ismail for their help in photography. I wish to extend my gratitude to my friends and colleagues Rogia, Rasha, Rasha, Eshtiag, Ikhlas, Ikhlas, Suheir, Naglaa, Huda, Nawal, Howida, Husham, Osama, Omer, and all my friends whom I did not mention, for their constant encouragement. My special gratitude and indebtedness are due to members of my family for their patience and understanding.

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CONTENTS

Acknowledgements.………………………………………………….…..……...i Contents.………………………………………………………………………...ii Introduction.…………………………………………………………….………1 Chapter One: Literature Review……………………………………………….3 I.1. Anatomical Study.……………………………………………………….3 I.1.1. The Lymph Nodes of the Head.…………………………….………..3 I.1.2. The Lymph Nodes of the Neck.…………………………….………..7 I.1.2.A. The Superficial Cervical Lymphocentre.…………………….…..7 I.1.2.B. The Deep Cervical Lymphocentre.………………………………8 I.1.3. Some Lymph Nodes of the …………………………………...9 I.1.3.A. The Dorsal Thoracic Lymphocentre.………………….………...9 I.1.3.B. The Mediastinal Lymphocentre.…………………………….….10 I.1.3.C. The Bronchial Lymphocentre.……………………….………...12 I.1.4. Some Lymphocentres and Nodes of the Abdominal and Pelvic Wall, Viscera and Hindlimb.…………………………..……...13 I.1.4.A. The Lumbar Lymphocentre.…………………………………...13 I.1.4.B. The Superficial Inguinal Lymphocentre…………………….….15 I.1.4.C. The Subiliac Lymph Nodes (Prefemoral)………………………15 I.1.4.D. The Tuberal …………………………………….16 I.1.4.E. The ………………………………….…16 I.2. Histology………………………………………………………………..20 I.2.A. The Lymph Nodes………………………………………………….20 I.2.A.1. The Capsule and Trabeculae…………………………………...20 I.2.A.2. The Parenchyma……………………………………………....22 I.2.A.2.A. The Cortex…………………………………………….…24 I.2.A.2.A.I. The Outer Cortex…………………………………...24 I.2.A.2.A.II. The Inner Cortex…………………………………..28

4 I.2.A.2.B. The Medulla……………………………………………...29 I.2.A.3. Lymph Circulation………………………………………….…30 I.2.A.3.A. Afferent Lymphatic Vessels……………………………...30 I.2.A.3.B. The System of the Lymph Sinuses………………………..31 I.2.A.3.C. The Efferent Lymphatic Vessels…………………………34 I.2.A.4. The Blood Circulation…………………………………………34 I.2.B. The Haemolymph Nodes…………………………………………...37 I.2.C. The Haemal Nodes………………………………………………....39 I.3.Electron Microscopy………………………………………………………42 I.4.Morphometry………………………………………………………………48 Chapter Two: Materials and Methods………………………………………..49 II.1. Gross Anatomy………………………………………………………….49 II.1.1. Materials……………………………………………………………49 II.1.2. Methods…………………………………………………………....49 II.1.2.A. Topography…………………………………………………..49 II.1.2.B. Weight………………………………………………………...49 II.1.2.C. Gross Features and Measurements……………………………49 II.1.2.D. Arterial Branches of the Mammary Lymph Node.……………50 II.2. Histological Study………………………………………………………..50 II.3. Technique for the Transmission Electron Microscope…………………..52 II.4. Morphometric Study…………………………………………………….53 Chapter Three: Results………………………………………………………..55 III.1.Gross Anatomy………………………………………………………...55 III.1.1.The Lymph Nodes of the Head………………………………….…56 III.1.1.A. The Parotid Lymphocentre…………………………………..56 III.1.1.A.1. The ………………………….…56 III.1.1.B. The Mandibular Lymphocentre……………………………...56 III.1.1.B.1. The Mandibular Lymph Nodes…………………………57 III.1.1.B.2. The Pterygoid Lymph Node……………………………57 III.1.1.C. The Retropharyngeal Lymphocentre…………………………58 III.1.1.C.1. The Medial Retropharyngeal Lymph Nodes…………….58

5 III.1.2. The ………………………………………..59 III.1.2.A.The Superficial Cervical Lymphocentre………………………59 III.1.2.A.1. The Dorsal Superficial Cervical Lymph Nodes………….59 III.1.2.A.2. The Ventral Superficial Cervical Lymph nodes………….59 III.1.2.B. The Deep Cervical Lymphocentre……………………………60 III.1.2.B.1. The Cranial Deep Cervical Lymph Nodes………………60 III.1.2.B.2. The Middle Deep Cervical Lymph Nodes………………62 III.1.2.B.3. The Caudal Deep Cervical Lymph Nodes………………63 III.1.3. Some Lymphocentres and Lymph Nodes of The Thorax…………64 III.1.3.A. The Intercostal Nodes……………………………………...64 III.1.3.B. The Thoracic Aorta Nodes…………………………………64 III.1.3.C. The Mediastinal Lymphocentre………………………….….64 III.1.3.C.1. The Cranial Mediastinal Lymph Nodes…………….….64 III.1.3.C.2. The Middle Mediastinal Lymph Nodes…………….….65 III.1.3.C.3. The Caudal Mediastinal Lymph Nodes…………….…..65 III.1.3.D. The Bronchial Lymphocentre………………………………66 III.1.3.D.1. The Right Tracheobronchial Lymph Node……………66 III.1.3.D.2. The Left Tracheobronchial Lymph Node……………..66 III.1.3.D.3. The Dorsal Tracheobronchial Lymph Node…………..67 III.1.4. Some Lymphocentres and Nodes of the Abdominal and Pelvic Wall, Viscera and Hindlimb………………………………...67 III.1.4.A. The Lumbar Lymphocentre……………………………….…67 III.1.4.A.1. The Lumbar Aortic Lymph Nodes………………….…..67 III.1.4.A.2. The Renal Lymph Nodes.………………………………67 III.1.4.B.The Superficial Inguinal Lymphocentre……………………….68 III.1.4.B.1.The Scrotal Lymph Node………………………………..68 III.1.4.B.2.The Mammary Lymph Nodes…………………………...68 III.1.4.C.The Subiliac Lymph Nodes (Prefemoral)………………….….70 III.1.4.D. The Tuberal Lymph Nodes………………………………….70 III.1.4.E. The Gastric Lymph Nodes………………………………….70 III.1.4.E.1. The Atrial Lymph Nodes………………………………70

6 III.1.4.E.2. The Right Ruminal Lymph Nodes……………………..70 III.1.4.E.3. The Left Ruminal Lymph Nodes………………………71 III.1.4.E.4. The Cranial Ruminal Lymph Nodes……………………71 III.1.4.E.5. The Reticular Lymph Nodes…………………………...71 III.1.4.E.6. The Omasal Lymph Nodes……………………………72 III.1.4.E.7. The Abomasal Lymph Nodes……………………….…72 III.2. Histology……………………………………………………………...73 III.2.I. The Lymph Nodes………………………………………………...73 III.2.I.1. The Capsule…………………………………………………..73 III.2.I.2. The Trabeculae……………………………………………….75 III.2.I.3. The Parenchyma……………………………………………...75 III.2.I.3.A. The Cortex……………………………………………...75 III.2.I.3.A.1. The Lymph Nodules…………………………….…75 III.2.I.3.A.1.A. The Primary Lymph Nodules...…….…….…..76 III.2.I.3.A.1.B. The Secondary Lymph Nodules………..….…76 III.2.I.3.A.2. The Diffuse Lymphoid Tissue……………………..77 III.2.I.3.B. The Medulla…………………………………………….78 III.2.I.4. The Lymph Circulation…………………………………….…79 III.2.I.4.A. The Afferent Lymphatic Vessels………………………...79 III.2.I.4.B. The Sinus System.……………………………………….79 III.2.I.4.C. The Efferent Lymphatic Vessels………………………...81 III.2.I.5. The Circumscribed Areas……………………………………..81 III.2.I.6. The Vascularization…………………………………………..82 III.2.II. The Haemal Nodes……………………………………………….84 III.3. Electron Microscopy…………………………………………………86 III.4. Morphometry…………………………………………………………93 Chapter Four: Discussion…………………………………………………....100 IV.1. Gross Anatomy………………………………………………………100 IV.1.1. The Lymph Nodes of the Head…………………………………..100 IV.1.2. The Cervical Lymph Nodes………………………………………102 IV.1.3. Some Lymphocentres and Lymph Nodes of The Thorax………...103

7 IV.1.4. Some Lymphocentres and Nodes of the Abdominal and Pelvic Wall, Viscera and Hindlimb…………………………...104 IV.2. Histology…………………………………………………………….107 IV.2.I. The Lymph and Haemolymph Nodes………………………….…107 IV.2.I.1. The Capsule and Trabeculae…………………………………108 IV.2.I.2. The Parenchyma…………………………………………….109 IV.2.I.3. The Lymph Circulation……………………………………...111 IV.2.I.4. The Vascularization………………………………………….115 IV.2.II. The Haemal Nodes………………………………………………116 IV.2.II.A. Gross Anatomy………………………………………….…116 IV.2.II.B. Histology…………………………………………………...116 IV.3. Electron Microscopy………………………………………………...119 IV.4. Morphometry………………………………………………………...122 Conclusions…………………………………………………………………..124 Summary……………………………………………………………………...125 Arabic Summary……………………………………………………………...129 References…………………………………………………………………….132 Legends of Figures…………………………………………………………...147

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9

INTRODUCTION

The habitat of the dromedary is Northern Africa, and the near East and West Central Asia (Wilson, 1984). Sudan is one of the most important countries in Africa regarding rearing and export of livestock. The most recent animal census estimated camel population in Sudan to be about 3 million. The dromedary population in Sudan ranks second to that of Somalia worldwide (AOAD, 2001).

The dromedary camel (Camelus dromedarius) is uniquely adapted to hot and arid environment. It produces milk, meat, wool, hair and hides and is used for riding, as an animal of burden and as a draft animal for agriculture and short distance transport (Schwartz and Dioli, 1992). Camels comprise about 6% of the number of animals used for the production of milk and meat in the Sudan. It’s meat constitutes about 9% of the national annual meat consumption. Trading in camels brings in about 25% of the national revenue of animal international trade (Haroon, 1991). The camel is an important component of the desert ecosystem .The ability of the camel to withstand adverse conditions is attributed to it’s adaptive physiological mechanisms aided by an array of supporting morphological features and behavioural attitudes (CRC, 2002). The camel is also known for it’s ability to resist diseases.

The significance of the study of lymph nodes of the camel lies in the important role played by them in the immune mechanism of the body. Camels suffering from a particular disease may show symptoms, which are rather different from symptoms shown by other animals to the same disease (Abdel-Magid, 1986). This indicates that the immune system in the camel may differ from that of other mammals. 10

The available literature reveals that there are some studies dealing with the structure of the lymph nodes of many domestic mammals including goat, sheep and ox (El-Gendi, 1971; Tanudimadja and Ghoshal, 1973; Ghoshal, 1976; Dhablania, Tyagi and Khatra, 1994; Sarma, Sarma and Goswami, 2001). On the other hand, there is little information about the lymph nodes of the camel (Taher, 1962; Smuts and Bezuidenhout, 1987). The ultrastructure of the lymph nodes of the camel is briefly studied by Abdel-Magid (1986), Osman (1988), Sharfee (1989), Osman, Elmaghrabi and Abugrian (1992) and Abdel-Magied, Taha, Al-Qarawi and Elfaki (2001).

The investigations included in the present study were undertaken with the aim of gaining a better knowledge of the topography, morphology and morphometry of the lymph nodes of the dromedary camel. Special attention was paid to the effect of age on the transformation of lymph nodes into haemolymph nodes. The findings of this work may, hopefully, stimulate other researchers to carry out further studies in the field of immunology in camels.

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CHAPTER ONE LITERATURE REVIEW

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CHAPTER ONE LITERATURE REVIEW I.1.Gross Anatomical Study

Many groups of lymph nodes or lymhocentres are found in the mammalian body, and the position of each group is relatively constant. Each group receives lymph from a specific region of the body (Rhodin, 1974). I.1.1. The Lymph Nodes of the Head The lymph nodes of the head region of domesticated animals are grouped into three lymphocentres: lymphocentrum partideum, lymphocentrum mandibulare and lymphocentrum retropharyngeum (El-Gendi, 1971; Tanudimadja and Ghoshal, 1973a; Sisson and Grossman, 1975; Dyce, Sack and Wensing, 1987; Smuts and Bezuidenhout, 1987; Hanger and Heath, 1991). The first group contains the parotid and accessory parotid lymph nodes. The second group includes the mandibular, buccal, pterygoid, submental, paramandibular and lingual lymph nodes. The third group comprises the medial retropharyngeal (suprapharyngeal and para pharyngeal), the lateral retropharyngeal (atlantal) and the hyoid (rostral and caudal) lymph nodes. It is pertinent to mention that not all these lymph nodes are present in all mammals (El-Gendi, 1971; Sisson and Grossman, 1975; Dyce et al., 1987; Hanger and Heath, 1991).

The parotid lymph nodes of domesticated animals are located between the caudal border of the masseter muscle and the rostral border of the parotid salivary gland, immediately below the mandibular articulation (Dyce and Wensing, 1971; El- Gendi, 1971; Sisson and Grossman, 1975; Dyce et al., 1987). Ramazanov (1976) reported that the parotid lymph nodes of the ox were situated in the nasolabial

13 region. Small accessory parotid lymph nodes were found in the buffalo (El-Gendi, 1971) and ox (Sisson and Grossman, 1975; Constantinescu, Broun and McClure, 1988). Constantinescu et al. (1988) added that the accessory parotid lymph nodes of the ox were divided into two types: one type was associated with a haemal node whereas the other type was not associated with a haemal node. The location of the parotid lymph nodes of the sheep and goat resembles in general that of the ox and the accessory parotid lymph node is found caudal to the main node and medial to the parotid salivary gland (May, 1970; Tanudimadja and Ghoshal, 1973a; El-Toum, 2000). In the horse (Sisson and Grossman, 1975; Dyce et al., 1987), the parotid lymphocentre consists of a superficial group of lymph nodes that are covered by or embedded in the parotid salivary gland. In the dog (Miller, Christensen and Evans, 1964; Chretien, Behar, Kohn, Moldovanu, Miller and Lawrence, 1967), the location of the parotid lymph nodes is similar to that of other domestic animals. The accessory parotid lymph nodes are absent. In the cat (Sisson and Grossman, 1975), the parotid lymph nodes are found in two groups near the temporomandibular articulation: one group is found in association with the superficial temporal vein and the other is found in association with the caudal auricular vein. Sugimura (1962) grouped the parotid lymph nodes of cats into cranial and caudal parotid lymph nodes. The parotid lymph nodes vary in number as follows: in the ox 1, sheep 2-4, goat 1-2, horse 6-10, dog 1-3 and pig 2-8. In buffalo calves (Dhablania et al., 1994) the number varies from 1 to 2. The available literature on the parotid lymphocentre of the dromedary was given by Taher (1962), Smuts and Bezuidenhout (1987), Osman (1988) and Abdel- Magied et al. (2001). Smuts and Bezuidenhout (1987) found that the parotid lymphocentre consisted of one or two superficial parotid lymph nodes situated at the dorsocranial border of the parotid salivary gland. Taher (1962) reported that the accessory parotid lymph nodes were absent.

14 The mandibular lymphocentre has been studied in ruminants, horse, dog, pig and cat by Taylor (1955), Sugimura (1962), Miller et al. (1964), Chretien et al. (1967), May (1970), Dyce and Wensing (1971), El-Gendi (1971), Evans and de- Lahunta (1971), Tanudimadja and Ghoshal (1973a), Romazanov (1976), Bagi, Vyas and Bhayani (1992), Dhablania et al. (1994), El-Toum (2000) and Sarma and Sarma (2000). The mandibular lymph nodes of mammals are generally described as superficial nodes found in the aboral part of the pharyngeal region, related to the angle of the mandible and covered only by the skin and cutaneous muscle (Sisson and Grossman, 1975; Dyce et al., 1987). In the goat (Sarma and Sarma, 2000), the mandibular lymph nodes are located about 2.5 cm. rostral to the angle of the mandible. El-Gendi (1971), Chretien et al. (1967), Sisson and Grossman (1975) and Dyce et al. (1987) reported the presence of additional, small accessory lymph nodes in buffalo, dog, pig and cat. Sisson and Grossman (1975) also reported the presence of haemal lymph node in some caprine species. In the ruminant, the lymph nodes of the mandibular lymphocentre are mainly found singly or not more than three lymph nodes on each side of the head (May, 1970; El-Gendi, 1971; Tanudimadja and Ghoshal, 1973a; Sisson and Grossman, 1975; Dhablania et al., 1994; El-Toum, 2000). In the horse, dog, cat and pig, more than one lymph node is present on each side of the head (Taylor, 1955; Miller et al., 1964; Chretien et al., 1967; Evans and de-Lahunta, 1971; Sisson and Grossman, 1975; Dyce et al., 1987). In the buffalo (El-Gendi, 1971) and ox (Sisson and Grossman, 1975), the pterygoid lymph nodes are related to the maxillary tuberosity and the pterygoideus muscle. In the camel (Taher, 1962; Smuts and Benzuidenhout, 1987), the mandibular lymphocentre consisted of the mandibular and pterygoid lymph nodes. Smuts and Benzuidenhout (1987) added that the was situated at the rostral border of the mandibular salivary gland in the intermandibular space, and the pterygoid lymph node was situated at the rostral border of the medial pterygoid

15 muscle. Abdel-Magied et al. (2001) reported that the mandibular lymph node measured 5.2cm. X4.3cm. X2.8cm..

Sisson and Grossman (1975) and Dyce et al. (1987) reported that the retropharyngeal lymphocentre in the ruminant, horse, dog and pig consisted of a medial and lateral retropharyngeal lymph nodes located on the dorsal wall of the pharynx, and the atlantic fossa, respectively. Sisson and Grossman (1975) recorded the presence of many smaller accessory lymph nodes with the medial retropharyngeal node. Ramazanov (1976) reported that the lateral retropharyngeal lymph nodes were situated in the nasolabial region in cattle. In the fallow deer (Dama dama) (Barrell and Simpson-Morgan, 1990), the distribution and size of the major lymph nodes of the head are similar to those of the nodes of sheep and goats. In the dog (Chretien et al., 1967; Sisson and Grossman, 1975; Dyce et al., 1987), the lateral retropharyngeal lymph node is related to the parotid salivary gland. The number of the lateral and medial retropharyngeal nodes in ox, sheep, goat, dog, cat, and pig varied from 1-2 nodes, and may reach 3 in ox and sheep and 8-15 in horse (May, 1970; Tanudimadja and Ghoshal, 1973a; Sisson and Grossman, 1975; El-Toum, 2000). In the camel, Taher (1962) recorded the presence of the so-called parapharyngeal lymph node and the absence of the atlantal and suprapharyngeal nodes. Moreover, innominate nodes were found in the vicinity of the hypoglossal muscle. Abdel-Magid (1986) reported the presence of the lateral retropharyngeal lymph node related to the mandibular salivary gland laterally and to the common carotid artery medially. Smuts and Bezuidenhout (1987) found that the retropharyngeal lymphocentre consists of 1-2 medial retropharyngeal lymph nodes situated between the jugular vein and the common carotid artery on the pharynx, and that the lateral ones are generally absent. Abdel-Magied et al. (2001) reported that the lateral retropharyngeal lymph node is larger than either the parotid or the mandibular lymph nodes, and measures about 6 cm. X 4.3 cm. X 2.2 cm..

16 I.1.2.The Lymph Nodes of the Neck The lymph nodes of the neck are grouped into superficial and deep cervical lymphocentres in the horse (Bradley, 1947), dog (Miller et al., 1964; Chretien et al., 1967), sheep (May, 1970), ox (Dyce and Wensing, 1971), buffalo (El-Gendi, 1971), goat (Tanudimadja and Ghoshal, 1973b) and camels (Smuts and Bezuidenhout, 1987). I.1.2.A.The Superficial Cervical Lymphocentre The superficial cervical lymphocentre comprises the superficial cervical (prescapular) lymph nodes and the accessory superficial cervical (nuchal) lymph nodes. In the ox (Sisson and Grossman, 1975), the superficial cervical lymph node is covered by the brachiocephalicus muscle; a few small accessory superficial cervical lymph nodes are found dorsal to the main node and associated with a number of small haemal nodes. Ghoshal (1976) recorded the presence of aberrant cervical lymph nodes seen on both sides in the caudal half of the neck in the ox. In the buffalo, El-Gendi (1971) gave a similar classification whereas Bagi et al. (1992) reported that the prescapular lymph node is very large when compared to most other lymph nodes. In the sheep (Sisson and Grossman, 1975), there are two smaller accessory superficial lymph nodes situated at the cranial border of the origin of the cervical part of the serratus ventralis muscle. May (1970) reported that the lymph nodes of the superficial cervical lymphocentre are divided into three groups: cranial, middle and caudal superficial cervical nodes. Haemal nodes are located near the hilus of the large node of the caudal one. In the pig where the neck is very short, the nodes of this centre may be mistaken with those of the head (Sisson and Grossman, 1975; Dyce et al., 1987). They are divided into three groups: a-Dorsal superficial cervical lymph nodes. b-Middle superficial cervical lymph nodes c-Ventral superficial cervical lymph nodes.

17 In the camel, a similar classification to that of the pig was given by Taher (1962). Smuts and Bezuidenhout (1987) reported that this centre in the camel is composed of two groups located cranial to the shoulder: a superficial dorsal, situated deep to the cleidocervical muscle, and a ventral one situated between the brachiocephalic and superficial pectoral muscles.

I.1.2.B.The Deep Cervical Lymphocentre This centre, in domestic animals, comprises three groups, namely: a-Cranial deep cervical lymph nodes, which lie at the beginning of the trachea close to the thyroid gland. b-Middle deep cervical lymph nodes, which are located at the middle of the cervical part of the trachea. c-Caudal deep cervical nodes, lie at the cervical part of the trachea just in front of the thoracic inlet. The previously mentioned groups of lymph nodes were described in the ox (Dyce and Wensing, 1971), buffalo (El-Gendi, 1971), sheep (May, 1970), goat (Tanudimadja and Ghoshal, 1973b), horse (Bradley, 1947) and dog (Bradley, 1927; Miller et al., 1964; Chretien et al., 1967). Tanudimadja and Ghoshal (1973b) and Sisson and Grossman (1975) reported the presence of a number of haemal nodes in the vicinity of the middle deep cervical lymph nodes in the ox and cranial ones in the goat. In the buffulo, El- Gendi (1971) recorded the presence of 2-3 small nodes as well as 3-4 haemal nodes with the main nodes of the cranial deep cervical lymph nodes, and 5-10 haemal nodes with the middle ones. On the left side, the oesophagus separated the nodes into two groups: the dorsal group, may be termed the paratracheal nodes, which contain 5-10 haemal nodes and the ventral group, or pretracheal nodes, containing 3-4 haemal ones. In the ruminant (Sisson and Grossman, 1975), two more lymph nodes are found, the costocervical lymph nodes which lie immediately in front of the first rib under the ventral scalenous muscle and the subrhomboid one which is found close

18 to the cervical angle of the scapula on the medial face of the cervical portion of the rhomboideus muscle. In the camel, Smuts and Bezuidenhout (1987) found that the deep cervical lymphocentre included the cranial, middle and caudal deep cervical lymph nodes and this classification is similar to that of other domestic animals.

I.1.3. Some Lymph Nodes of the Thorax The available literature shows that the lymph nodes of the thorax are classified into parietal and visceral groups. The parietal group comprises three lymphocentres: dorsal thoracic, ventral thoracic and mediastinal lymphocentres. The visceral group constitutes the bronchial lymphocentre.

I.1.3.A. The Dorsal Thoracic Lymphocentre The dorsal thoracic lymphocentre constitutes the intercostals and thoracic aortic lymph nodes. The intercostal lymph nodes are common in the horse, ox, sheep and goat, occasionally in dog and cat and absent in pig (Chretien et al., 1967; May, 1970; Sisson and Grossman, 1975). In the buffalo (El-Gendi, 1971) and sheep (May, 1970), the intercostal nodes are related to the deep face of the external intercostal muscle, and the nodes of the sixth or seventh to the tenth intercostal spaces are inconstant. In the horse (Sisson and Grossman, 1975), the lymph nodes located in the first and second intercostal spaces and are named cranial mediastinal lymph nodes. In the dog (Chretien et al., 1967), the left intercostal lymph node is situated adjacent to the thoracic duct at the level of the eightth intercostal space. Sisson and Grossman (1975) added that these nodes are located in the region of the fifth or sixth intercostal space near the head of the rib. In the camel, the intercostal lymph nodes are reported by Taher (1962). Smuts and Bezuidenhout (1987) found that the intercostal nodes are inconstant and situated dorsal to the sympathatic trunk in the 4th-6th intercostal spaces.

19 The thoracic aortic lymph nodes are present in all domesticated animals except the dog (Sisson and Grossman, 1975). They are embedded in fat and located along the dorsolateral border of the thoracic aorta and ventral to the sympathatic nerve trunk in ruminants and the horse, and related to the azygous vein in the pig and cat. In the buffalo (El-Gendi, 1971), the nodes of the right side show a more regular arrangement; they lie dorsal to the thoracic duct at the level of the ninth to the twelfth ribs, and the last two nodes are accompanied by two haemal nodes. The nodes of the left side are situated cranial and dorsal to the vena hemiazygos at the level of the heads of the sixth to eighth ribs, and the most cranial node is accompanied by a haemal node. In the sheep, the presence of numerous haemal nodes in the vicinity of the lymph nodes were reported by May (1970) and Sisson and Grossman (1975). In the goat, the cranial node of the thoracic aortic lymph nodes was seen at the level of the fifth intercostal space (Sisson and Grossman, 1975), whereas in the pig (Sisson and Grossman, 1975; Dyce et al., 1987), the nodes are located caudal to the sixth rib. In the camel, the distribution of the thoracic aortic nodes is similar to that in ruminants and the horse (Smuts and Bezuidenhout, 1987).

I.1.3.B. The Mediastinal Lymphocentre The mediastinal lymphocentre is composed of the mediastinal lymph nodes, which are situated in the mediastinum, and are subdivided in the domestic mammals into cranial, middle and caudal groups (Sisson and Grossman, 1975; Dyce et al., 1987). The cranial mediastinal lymph nodes in most domestic animals comprise a large number of relatively small nodes scattered in the cranial mediastinum in association with the large blood vessels, and occasionally, the trachea and oesophagus (May, 1970; Sisson and Grossman, 1975; Dyce et al., 1987).

20 In the buffalo (El-Gendi, 1971), the cranial mediastinal lymph nodes on the right side are classified into five groups, while those of the left side are generally smaller in size and less in number and are present in four groups.

The middle mediastinal lymph nodes are located in the middle mediastinum dorsal to the base of the heart or the aortic arch and extend to the right face of the oesophagus. They are absent in sheep, pig, dog and cat (Sisson and Grossman, 1975). In the ox (Dyce and Wensing, 1971; Dyce et al., 1987), the middle mediastinal nodes may not be clearly distinguishable from the cranial and caudal mediastinal lymph nodes, and in the horse they are indistinguishable from the thoracic aortic lymph nodes. El-Gendi (1971) reported that the middle mediastinal lymph nodes in the buffalo consist of two nodal groups: the cranial group is placed cranial to the aortic arch, dorsal to the oesophagus and ventral to the longus colli muscle, and the caudal group is aggregated caudal to the aortic arch and dorsal to the oesophagus along with the dorsal division of the vagus nerve. In the goat (Tanudimadja and Ghoshal, 1973c), the middle mediastinal nodes are found between the oesophagus and the longus colli muscle between the third to fifth ribs. In the ox, Dyce and Wensing (1971) reported the presence of other lymph nodes, which they described as ventral mediastinal nodes. They lie in the mediastinum towards its sternal attachment, mainly in the angle between the breastbone and the diaphragm. In the buffalo (El-Gendi, 1971), these nodes extended from the level of the eighth, or ninth thoracic vertebra to the last ones. In the camel, Taher (1962) divided the mediastinal lymph nodes into dorsal, cranial and caudal nodes, but the ventral mediastinal group is absent. Smuts and Bezuidenhout (1987) found that the mediastinal lymph nodes included the cranial, middle and caudal mediastinal lymph nodes and this classification is similar to that in other domestic animals.

21 I.1.3.C. The Bronchial Lymphocentre Sisson and Grossman (1975) and Dyce et al. (1987) included the visceral lymph nodes of the thorax in most domestic animals in one centre, the bronchial lymphocentre. They divided the bronchial lymph nodes into the left, right, middle, cranial and caudal tracheobronchial, pulmonary, right and left pericardial and diaphragmatic lymph nodes. In the buffalo, El-Gendi (1971) reported that the bronchial lymphocentre comprises two collections of nodes, the first group is the bronchial nodes which are placed in relation to the pulmonary and tracheal bronchi and comprise the right, left and dorsal or middle bronchial and cranial lymph nodes, the other group is the pericardial lymph nodes which are associated with the pericardium. In the sheep, May (1970) reported that the bronchial lymph nodes are grouped into cranial and caudal groups. In the horse (Bradley, 1946), the bronchial lymph nodes are situated at the dorsal and ventral aspects of the bifurcation of the trachea and the initial part of the bronchi.

In most domestic animals, the left tracheobronchial lymph nodes lie in the angle between the aortic arch and the left division of the pulmonary artery. In the horse and dog, they are related to the left face of the tracheal bifurcation, and in ruminants and pig to the left azygos vein (Sisson and Grossman, 1975). In the dog, Chretien et al. (1967) reported the presence of the left bronchial and left tracheal lymph nodes; the latter-mentioned nodes lie cranial to the first node.

The right tracheobronchial lymph nodes, in most domestic animals, are related to the right cranial bronchus on the lateral and dorsolateral side of the tracheal bifurcation. These nodes are absent in the domestic ruminants (Sisson and Grossman, 1975).

22 In the buffalo, El-Gendi (1971) reported that the right tracheobronchial nodes are placed at the hilus of the right lung along the pulmonary vessels and bronchi and are grouped into cranial, middle and caudal groups. Chretien et al. (1867) found in the dog additional nodes in the cranial mediastinum close to the azygos vein, and tracheal nodes and which they named as the right tracheal, bronchial and right bronchial lymph nodes.

In most domestic animals the pulmonary nodes are located along the course of the chief bronchi. They are absent in sheep and pig and inconstant in the ox, goat and horse (Sisson and Grossman, 1975).

The pericardial lymph nodes are usually bilaterally placed in the buffalo although their presence on the right side is not constant and the pulmonary node is absent (El-Gendi, 1971). In the goat, Sisson and Grossman (1975) reported the presence of the left pericardial lymph nodes and the absence of the right ones. The left pericardial nodes are inconstant; when present they lie on the base of the pericardium near the site of penetration of the left azygos vein through the pericardium. In the camel, Taher (1962) reported the occurrence of the right and left bronchial nodes. Smuts and Bezuidenhout (1987) reported that the left tracheobronchial lymph nodes are situated between the left bronchus and the aortic arch, the middle one is dorsally placed on the bifurcation of the trachea and the right one is absent.

I.1.4. Some Lymphocentres and Nodes of the Abdominal and Pelvic Wall, Viscera and Hindlimb I.1.4.A. The Lumbar Lymphocentre

23 The lumbar lymphocentre comprises the lumbar and renal lymph nodes in most domestic animals (Sisson and Grossman, 1975). In the buffalo this centre is characterised by the abundance of small haemal nodes in the vicinity (El-Gendi, 1971). In the cat, the lumbar group includes the cranial and caudal lumbar lymph nodes (Sugimura, 1962). The lumbar nodes are situated along the course of the caudal vena cava and abdominal aorta; they are termed the aortic lumbar lymph nodes. In cattle and buffalo, additional nodes are occasionally present between the lumbar transverse processes, and are called the proper lumbar lymph nodes (El-Gendi, 1971; Sisson and Grossman, 1975). Dyce et al. (1987) stated that the nodes spread along the psoas musculature. In the dog, Miller et al. (1964) and Sisson and Grossman (1975) stated that the lumbar nodes are embedded in adipose tissue, and because of their small size and similarity in colour to the fat, they may escape notice. In the camel, the aortic lumbar lymph nodes were demonstrated by Taher (1962) and Smuts and Bezuidenhout (1987).

The renal lymph nodes in most domestic animals (Sisson and Grossman, 1975; Dyce et al., 1987) are associated with the renal vessels, and some of the lymph nodes are located at the renal hilus in the ox, horse and pig, and embedded in adipose tissue in the horse. May (1970), Chretien et al. (1967) and Sugimura, Kudo and Takahata (1958) agreed that the renal lymph nodes of the sheep, dog and cat are similar to those of other domestic animals. In the buffalo (El-Gendi, 1971), the renal nodes are subdivided into right and left nodes. The right renal nodes include two sets: the first set is related to the right renal artery and the second set is scattered around the right adrenal gland and named as the adrenal nodes. The left renal lymph nodes are divided according to their position into three groups: the first group is related to the abdominal aorta and caudal vena cava, the second group lies cranial to the first and in relation to the

24 left adrenal gland and the third group lies along the medial surface of the kidney. Many haemal nodes are found around all the groups mentioned above. In the camel (Smuts and Bezuidenhout, 1987), the renal lymph nodes are found along the renal blood vessels. I.1.4.B. The Superficial Inguinal Lymphocentre Sugimura, Kudo and Takahata (1956), Chretien et al. (1967), May (1970), El- Gendi (1971), Sisson and Grossman (1975) and Dyce et al. (1987) reported that this centre is represented in male mammals by the scrotal lymph nodes. They are situated caudal to the spermatic cord along the dorsolateral border of the penis and in some animals they are related to the external pudendal vessels. In the female of most domestic mammals, the mammary lymph nodes lie at the caudodorsal part of the udder either inbetween the ventral portion of the abdominal wall and the udder (mare) or between the thigh and the udder (cow). They are related to the external pudendal vessels as they leave the abdominal wall. The arterial supply to the mammary lymph node was studied by Heath and Brandon (1983) and Heath, Brandon and Fogarty (1985) in sheep and Spalding and Heath (1986) in the pig. In the cat (Sugimura et al., 1956), buffalo (El-Gendi, 1971), horse (Sisson and Grossman, 1975) and pig (Dyce et al., 1987), other inconstant nodes, termed as accessory superficial , are described. In the ox (Dyce and Wensing, 1971; Hampl, 1978), the presence of intramammary lymph nodes is reported. In the camel, Taher (1962) and Smuts and Bezuidenhout (1987) found that the superficial inguinal lymphocentre is represented in male by the scrotal nodes and in female by the mammary nodes and this classification is similar to that of other domestic animals. The former author considered the nodes as belonging to the pelvic limb.

I.1.4.C. The Subiliac Lymph Nodes (Prefemoral)

25 In all domestic mammals the subiliac lymph nodes are located in the flank region near the cranial border of the thigh. They are situated on the aponeurosis of the external oblique abdominal muscle, in contact with the tensor fasciae latae muscle between the patella and coxal tuber (Sisson and Grossman, 1975; Dyce et al., 1987). Occasionally in the ox a second small lymph node is present dorsal or ventral to the large one (Sisson and Grossman, 1975). El-Gendi (1971) considered these small nodes as separate nodes that belong to the prefemoral Lymphocentre in the buffalo. In sheep, May (1970) named this node as precrural node. Taher (1962) and Smuts and Bezuidenhout (1987) did not mention the presence or absence of these lymph nodes.

I.1.4.D. The Tuberal Lymph Node It is occasionally found in ruminants on the medial side of the ischiatic tuber near the attachment of the broad sacrotuberal ligament and covered by skin. In the pig, dog and cat, these nodes are absent (Sisson and Grossman, 1975; Dyce et al., 1987). In sheep, they are divided into two groups, one cranial to the tuber ischii and the other caudal and medial to the tuber (May, 1970). In the camel, the tuberal lymph nodes lie under the skin at the caudal border of the sacrotuberal ligament (Smuts and Bezuidenhout, 1987).

I.1.4.E. The Gastric Lymph Nodes May (1970), El-Gendi (1971), Sisson and Grossman (1975) and Saleh and Ibrahim (1975) grouped the ruminant gastric lymph nodes into atrial, ruminal, reticular, abomasal, ruminoabomasal and reticuloabomasal lymph nodes corresponding to the different compartments of the .

The atrial lymph nodes lie chiefly on the visceral surface of the atrium just caudal to the cardia (Sisson and Grossman, 1975; Saleh and Ibrahim, 1975) . Dyce

26 et al. (1975) recorded that these nodes were situated between the cardia and omasum. In the sheep, the atrial lymph nodes are not clearly distinguishable from the omasal lymph nodes (May, 1970; Sisson and Grossman, 1975).

The ruminal lymph nodes are grouped according to their location on the rumen into right, left and cranial ruminal lymph nodes. The right ruminal lymph nodes, 2-6 in number, lie along the course of the right ruminal artery and are related to the right longitudinal groove (Sisson and Grossman, 1975; Saleh and Ibrahim, 1975). In the buffalo, El-Gendi (1971) divided the right ruminal lymph nodes into three isolated groups in addition to small lymph nodes near the ruminoomasal junction. These small lymph nodes are known as the accessory right ruminal lymph node (Sisson and Grossman, 1975). In the goat, the ruminal lymph nodes are represented by 15-18 nodes and are considered as the caudal continuation of the atrial nodes (Sisson and Grossman, 1975). The left ruminal lymph nodes were inconstant and are found in the left longitudinal groove of the rumen (May, 1970; Sisson and Grossman, 1975; Saleh and Ibrahim, 1975). In the buffalo, El-Gendi (1971) described the left ruminal lymph nodes in addition to very small nodes at the left end of the caudal ruminal groove and are considered as the caudal ruminal lymph nodes. The cranial ruminal lymph nodes are embedded deeply in the cranial ruminal groove in the ox and sheep but are absent in the goat (May, 1970; Sisson and Grossman, 1975; Saleh and Ibrahim, 1975).

In the ox and sheep, the reticular lymph nodes are situated on the reticulum, dorsal and ventral to its junction with the omasum, whereas in the goat they are located in the ruminoreticular groove (May, 1970; Sisson and Grossman, 1975). In the buffalo, El-Gendi (1971) recorded that the greater number of the reticular lymph nodes constitute the dorsal group and some of them lie more to the

27 left than to the dorsal aspect of the reticulum and the cranial group is located on the cranial end of the right face of the reticulum. Saleh and Ibrahim (1975) named the ventral group as reticuloabomasal lymph nodes, which are located in the reticuloabomasal groove. In the ox and sheep, the omasal lymph nodes lie on the omasum chiefly along the course of the left gastric vessels and in the goat they lie on the right side of the rumen along the dorsal curvature of the omasum (May, 1970; Sisson and Grossman, 1975). In the buffalo, the omasal lymph nodes are grouped around the branches of the omasoabomasal vessels on the omasum (El-Gendi, 1971; Saleh and Ibrahim, 1975).

The dorsal abomasal lymph nodes are located along the lesser curvature of the abomasum (May, 1970; Sisson and Grossman, 1975). In the buffalo (El-Gendi, 1975), the abomasal nodes are continuous with the duodenal lymph nodes. Saleh and Ibrahim (1975) added that they are located along the course of the dorsal abomasal vessels. In the goat the abomasal nodes are sometimes embedded in fat between the origin of the abomasum and omasum (Sisson and Grossman, 1975).

The ventral abomasal nodes are sometimes absent; when present they are located in fat along the greater curvature of the pyloric part of the abomasum or in the omentum (May, 1970; Sisson and Grossman, 1975; Saleh and Ibrahim, 1975). In the buffalo and cattle, these nodes are often difficult to find in the mass of fat in which they are embedded (El-Gendi, 1971; Sisson and Grossman, 1975). The ruminoabomasal nodes are present only in the ox. They are located on the left side of the proximal half of the abomasum in a groove between the abomasum and ventral sac of the rumen. Caudally these lymph nodes are not clearly distinguishable from the ventral abomasal lymph nodes and dorsocranially they may not be easily differentiated from the reticuloabomasal lymph nodes (Sisson and Grossman, 1975).

28

In the ox, the reticuloabomasal nodes appear to be a craniodorsal extension of the rumino-abomasal lymph nodes. They are located in the angle formed between the reticulum, omasum, abomasum and the rumen. In the goat, they are located between the two layers of the omentum along the greater curvature of the abomasum and reticulum (Sisson and Grossman, 1975).

The gastric lymph nodes of the horse and pig are situated at the lesser curvature of the stomach near the cardia being associated with the left gastric artery in the horse and the right one in the pig. Occasionally, they are undistingwishable from the caeliac lymph nodes (Sisson and Grossman, 1975; Dyce et al., 1987). In the horse, some of these nodes are related to the ventral aspect of the pylorus (Bradley, 1946).

In the camel, Taher (1962) gave a detailed description of the gastric lymph nodes and grouped them as dorsal and right ruminal and dorsal and ventral omasoabomasal lymph nodes. He also reported the presence of dorsal and ventral abomasal lymph nodes. The omasal lymph nodes were not mentioned in the camel. Smuts and Benzuidenhout (1987) divided the gastric lymph nodes into several groups. These groups are the right ruminal, left ruminal, cranial ruminal, reticular, omasal and abomasal lymph nodes.

I.2. Histology

29 It appears from the available literature that the histology of the lymph nodes, haemolymph nodes and haemal nodes of many mammals, including man, have been extensively investigated. They are structurally related to peripheral lymphoid organs, and resemble each other in having nodular and diffuse lymphoid tissue, although they have different types of sinuses namely lymph, blood or haemolymph sinuses (Banks, 1993; Abbas, Lichtman and Pober, 1994).

I.2.A. The Lymph Nodes These nodes are enclosed within a dense connective tissue capsule. The capsule sent trabeculae into the parenchyma and subdivided it into compartments. The parenchyma in turn is subdivided into cortex and medulla. The cortex is organized in the form of lymph nodules and diffuse lymphoid tissue (Leeson and Leeson, 1970; Koss, 1992; Fawcett, 1994; Junqueira, Carneiro and Kelley, 1998). I.2.A.1. The Capsule and Trabeculae The capsule and trabeculae of the lymph node of mammals consist primarily of dense irregular collagenous connective tissue with some elastic and reticular fibres and a few smooth muscle fibres (Folse, Beathard and Granholm, 1975; Dellmann and Brown, 1981; Constantinescu et al., 1988; Young and Heath, 2000). In the goat, Faroon, Henry and al-Bagdadi (1987) reported the presence of smooth muscle cells in the trabeculae and capsule of several superficial lymph nodes like the mammary, mandibular, popliteal, subiliac and superficial cervical lymph nodes. In inguinal lymph nodes of the man and rat, the capsule adjacent to the lymph nodules contains smooth muscle fibres oriented in different directions and are in close contact with each other. At the entrance of afferent lymphatic vessels into the capsule, the fibres are circularly arranged in a spiral manner to form a muscular constrictor (Pastukhova, 1986). In the cat lymph nodes, the capsule is usually thin so that no regional differences can be found; it becomes thicker with advancing age (Sugimura, 1962).

30 The capsule of the lymph nodes of neonatal mice is loose and thick, and becomes thinner with maturation (Hwang, Sugimura, Othaishi and kudo, 1968). In the rat, the surface of the capsule is either smooth or variably indented; the latter condition is encountered predominantly in the mesenteric nodes. The capsule on the convex side of the node is pierced by a number of afferent lymphatic vessels (Denz, 1947; Kessel, 1998). The capsule is surrounded by adipose tissue (Downey, 1965; Gartner and Hiatt, 1997), which is plenty or thick in women than in men (Sapin, 1977). Denz (1947) reported that the capsule in the faetal node is separated from lymphoid tissue by the marginal sinuses but after puberty this separation may become incomplete. The capsule is thickest at the hilus, where it surrounds the blood and lymph vessels (Fawcett, 1994; Gartner and Hiatt, 1997). In the pig, a definitive hilus is not always seen; there is microscopic hilus- like indentations wherever afferent lymphatic vessels enter (Dellmann and Brown, 1981). Pig lymph nodes lack a typical hilus (Spalding and Heath, 1986). In human mesenteric lymph nodes there are two or three hiluses (Gavrichenkova, 1982). From the capsule, trabeculae of similar structure extend into the parenchyma. The trabeculae may extend to the hilus and are surrounded by the subtrabecular sinuses (Anderson, 1972; Cormack, 1997; Underwood, 2000). In cats (Sugimura, 1962), the trabeculae may be absent and the trabecular system in superficial lymph nodes is more developed than that in the deep ones. Prominent fibrous trabeculae are present in most of the lymph nodes of the pig (Hunt, 1968). In the human inguinal lymph nodes, the trabeculae seem to be poorly developed at all ages and during childhood the deep cervical nodes show well- developed trabeculae and in extreme old age the trabeculae are almost lacking. The large peripheral lymph nodes have prominent trabeculae that extend inward from the cortex but in small nodes the trabeculae are thin and often interrupted, whereas

31 the nodes deep in the body, as in the abdominal cavity, have relatively poorly developed trabeculae (Fawcett, 1994).

In the camel, Osman (1988) reported that a thick capsule of dense irregular connective tissue mainly collagenous fibres surrounds the mammary and parotid lymph nodes but smooth muscle fibres are absent. Sharfee (1989) reported that the capsule of each lobule of the node is thin and consists mainly of collagenous and elastic fibres. Abdel-Magied et al. (2001) found that smooth muscle fibres are occasionally encountered within the capsule and septa of the parotid, mandibular and lateral retropharyngeal lymph nodes.

I.2.A.2. The Parenchyma The parenchyma of the lymph node in many mammals is divided into an outer cortex and an inner medulla (Sugimura, 1962; Ross, Romrell, and Kaye, 1995; Old and Deane, 2001). The cortex usually surrounds the medulla except at the hilus (Leeson and Leeson, 1970). In human, the distinction between the cortex and medulla is relatively easy in the superficial nodes but more difficult in the deep ones (Denz, 1947). The compartments are not so definite as in many lower mammals (Leeson and Leeson, 1970). The amount of parenchyma in the node decreases with age and the correlation between the medullary and cortical substance also changes (Sapin, 1977). After puberty, the cortical tissue decreases in amount; in senility the cortical tissue consists of islands surrounded by medullary tissue and in extreme old age the deep cervical nodes may resemble those of the fetus in their simplicity of structure, for the cortex and medulla may again appear as continuous units, without nodules (Andrew, 1971). In the bovine intramammary lymph nodes in early fetal period, the differentiation into cortex and medulla is not obvious (Hampl, 1978). The young, mature and middle-aged rats show gradually increasing size of the medulla with a concomitant decrease in width of the cortex (Andrew, 1971).

32 The pig is the only domestic mammal in which lymph nodes have a reverse pattern to that observed in other species (Dellmann and Brown, 1981; Merighi, Galloni and Gobetto, 1986; Spalding and Heath, 1986; Banks, 1993). The parenchyma is clearly divided into two tissues: cortex-like tissue and medulla-like tissue. The cortex-like tissue is located not only in the central area of the nodular units but also in the subcapsular area around the A-type hilus at which afferent lymph vessels enter the node (Hoshi, Hashimoto, Kitagawa, Kon, and Kudo, 1986). The lymph nodes of dolphins, hippopotamuses, rhinoceroses and domestic pigs are different from those of other domestic mammals in that their lymph nodes consist of several nodules and the cortex of each nodule is located toward its centre and the medulla is at the periphery (Tizard, 2000).

The camel lymph nodes show lobulation and the lobules are separated from each other by complete or incomplete connective tissue septae. The nodal parenchyma is difined into a cortex and medulla (Osman, 1988; Sharfee, 1989). The parenchyma consists of lymph nodules, anodular lymphoid tissue formed of patches of variable size that often contact the lymph nodules (Abdel-Magied et al., 2001). The parenchyma is supported by connective tissue framework consisting mainly of a network of reticular fibres and some collagenous fibres (Osman, 1988; Sharfee, 1989). The reticular fibres are present in the dense anodular and diffuse lymphoid tissue of the parenchyma (Abdel-Magied et al., 2001). Osman (1988) and Sharfee (1989) agreed that the term mixed lymph nodes is most appropriate for the camel lymph node. Sharfee (1989) divided the nodes into primary and secondary mixed lymph nodes. The cortex mereges with the medulla without clear demarcaion in the primary mixed lymph nodes but in the secondary ones there is a distinct but irregular line of demarcation.

I.2.A.2.A. The Cortex

33 The cortex of the lymph nodes appears as a dense mass of lymphoid tissue traversed by the trabeculae and lymph sinuses. The cortex is divided into two regions: an outer cortex and an inner deep one and there is no distinct boundary between them (Dellmann and Brown, 1981; Fawcett, 1994; Junqueira et al., 1998; Young and Heath, 2000). The superficial and deep cortices are also termed thymus- independent and thymus-dependent areas, respectively (Unanue and Benacerraf, 1984). In dolphins, hippopotamuses, rhinoceroses and domestic pigs, the cortex and paracortex have a similar structure to that in other mammals (Tizard, 2000). Generally the cortex of the cat lymph nodes is well developed and only in the mediastinal group is the cortex poorly developed. Irregularity in the arrangment of the cortex is occasionally found in the lymph nodes and is more often observed in the retropharyngeal, small intestinal and large intestinal groups than in other ones (Sugimura, 1962). In the rat, the node is either a segmented or a non-segmented one. In the segmented node, the subcapsular sinus within the peripheral cortex is separated by gaps in which medullary sinuses reach the capsule but in the nonsegmented node the cortex appears as a continuous layer (Sainte-Marie, Peng and Belisle, 1982). In the dog, the lymph nodules of tracheobronchial lymph nodes contain a substantial number of blood capillaries forming a vascular network with more density in the secondary than in the primary lymph nodules (Salvador, Pereira, de Sa and Grande, 1992b). Belz and Heath (1995b) recorded that within the cortex a network of arterioles, capillaries and venules occur near subcapsular and trabecular sinuses and around the nodules but the nodules themselves are relatively avascular.

I.2.A.2.A.I. The Outer Cortex In the outer cortex, lymphocytes form diffuse lymphoid tissue and a variable number of densely packed lymph nodules that have traditionally been classified as primary and secondary lymph nodules (Koss, 1992; Ross et al., 1995; Beniamini, Sunshine and Leskowitz, 1996; Weir and Stewart, 1997). The outer cortex is

34 separated from the capsule and trabeculae by the lymph sinuses (Leeson and Leeson, 1970; Junqueira et al., 1998). In the horse, a fusion of cortical nodules is common (Banks, 1993). In the pig, the cortex consists of unorganized lymphoid tissue and sinuses (Dellmann and Brown, 1981; Banks, 1993). In man, a fine stroma of reticular cells and fibres permeates the nodule (Rhodin, 1974). The outer cortex is formed of a network of reticular cells and fibres whose meshwork is populated by B-cells (Junqueira et al., 1998). The primary lymph nodules are spherical or ovoid areas of tightly packed small lymphocytes that are devoid of germinal centres (Banks, 1993; Fawcett, 1994; Ross et al., 1995; Cormack, 1997; Gartner and Hiatt, 1997). They are composed of a mesh of follicular dentritic cells whose spaces are filled with recirculating resting small B-lymphocytes (Roitt, 1997). In man and laboratory rodents, the primary nodules consist merely of lymphoid tissue intervening between the secondary nodules of the outer cortex. In other species, notably the ox, the primary nodules appear as discrete rounded aggregates that may project slightly above the surface of the node (Fawcett, 1994). The secondary lymph nodules are spherical with two zones: a light and dark zones in cats (Rohlich, 1930, 1933), rats (Kindred, 1938), mice (Congdon, 1962), man (Millikin, 1966) and pig (Hunt, 1968). In the cat (Sugimura, 1962), the reticular fibres are distinct in the corona but scanty in the germinal centre of the nodules. Hunt (1968) reported that the light zone of porcine germinal centre is not clearly distinguishable from the dark zone. Moreover, the germinal centres related to the trabeculae have their light zones facing the trabeculae, often with a cap of lymphocytes on that side. The secondary lymph nodules have a paler central zone called germinal centre and an outer corona (Leeson and Leeson, 1970; Fawcett, 1994; Rizzo, 2001). The germinal centres have paler staining cells than the corona; this is because the large lymphocytes and macrophages, which are found at the centre, have more cytoplasm than the small ones and their nuclei are more euchromatic (Leeson and Leeson, 1970; Fawcett, 1994). Banks (1993) attributes the paler

35 staining to the presence of fewer cells in the germinal centres in comparison to the corona. In the horse lymph node (Heath and Nikles, 1991), there are no constant relationship between the number of the nodules and the location of the node. Moreover, the secondary nodules are usually surrounded by a network of lymph sinuses. In the camel, the majority of lymph nodules have a large germinal centre and narrow corona (Osman, 1988; Sharfee, 1989; Abdel-Magied, et al., 2001). Osman (1988) added that the nodules are situated at the periphery of the lobules below the capsule and on either side of the trabeculae in all parts of the lymph node. The nodules are supported by a network of a large number of reticular cells with long cellular processes and a few elastic fibres. Osman (1988) and Abdel-Magied et al. (2001) agreed that the lymph nodules are devoid of reticular fibres. Arterioles and capillaries are found inside the lymph nodules (Osman, 1988). Leeson and Leeson (1970) reported that most of the cells of the germinal centre are medium-size lymphocytes; a few are large, undifferentiated lymphocytes and plasma cells. The large lymphocytes are known as lymphoblasts (Rhodin, 1974). Banks (1993) recorded that mature lymphocytes and lymphoblasts are the dominant cell types although plasma cells and macrophages are also present. The germinal centre may contain large lymphocytes and macrophages (Fawcett, 1994). The activated B.cells in the germinal centre are collectively called follicle centre cells. They are characterized by light nuclei and have more cytoplasm and are less densely packed than the smaller, more peripheral follicular B cells. This explains the lower staining intensity of the germinal centre (Stevens and Lowe, 1997). Some cells of the germinal centre differentiate into plasmablasts and migrate to become plasma cells in the medullary cords and project between the medullary sinuses (Roitt, 1997). Germinal centres occur in a variable number in the outer cortex but are seldom found in the inner cortex and quite rare in the medulla. Those located in the outer cortex are polarized in such a way that their light region and cap are

36 directed toward the marginal sinuses, which receive the incoming lymph (Fawcett, 1994). The germinal centres of the lymph nodes of pigs show a reversal of the microanatomy of the nodes of other mammals and this reflects the unusual direction of the lymph flow (Hunt, 1968). In man, the germinal centres seem to be poorly developed in the inguinal lymph nodes at all ages. During childhood the deep cervical nodes show well- developed germinal centres; there is some decrease in size after puberty because of retrogressive changes in the germinal centres (Andrew, 1971). Germinal centre formation, particularly evident in infants and children, less in young adults and often absent in aging individuals, is most impressive in lymph nodes normally exposed to antigenic stimulation (Luscieti, Hubschmid, Cottier, Hess and Sobin, 1980). In the camel, large and small lymphocytes and plasma cells are found in the germinal centres (Osman, 1988). Large and medium-sized lymphocytes, a few plasma cells and lymphocytes with mitotic figures are present (Sharfee, 1989). The germinal centres contain small and medium-sized lymphocytes, dividing and undividing lymphoblasts, plasma cells, reticular cells and non-fenestrated blood capillaries. Thick basal laminae and pericytes often surround the nodular blood capillaries (Abdel-Magied et al., 2001). The corona consists of small and densely packed lymphocytes that surround the germinal centre of secondary nodules (Fawcett, 1994; Cormack, 1997; Underwood, 2000). The small lymphocytes are produced by the cells of the germinal centres and are pushed outward into a peripheral zone, which becomes the cortex of the nodules. Fawcett (1994) added that this form is referred to as the mantle or crescent. In the cat, the dark zone is cap-shaped and faces the capsule (Sugimura, 1962). In the camel, the corona is occupied mainly by small lymphocytes (Osman, 1988; Sharfee, 1989). It contains closely packed cells that are often distinctively flattened (Abdel-Magied et al., 2001).

37 The diffuse lymphoid tissue constitutes the internodular cortex and the inner or deep cortex (Koss, 1992; Fawcett, 1994). A few T-cells are found in the cortex, in a region immediately surrounding each secondary lymph nodule (Tizard, 2000). In the cat, the reticular meshes of the cortex are wide and polygonal in shape (Sugimura, 1962). The dense lymphatic tissue in the camel consists of lymphocytes of various sizes, plasma cells, reticular cells, erythrocytes and a few macrophages (Sharfee, 1989).

I.2.A.2.A.II.The Inner Cortex The inner cortex is devoid of lymph nodules (Burkitt, Young and Heath, 1997; Yound and Heath, 2000). It continues into the medullary cords without any discernible demarcation (Fawcett, 1994; Ross et al., 1995; Gartner and Hiatt, 1997). In the germ-free mouse, the deep cortex of the mesenteric nodes is composed of semi-rounded units and each one comprising a centre and a periphery. This fact is different from that of the other nodes found in the same animals (Sainte-Marie and Peng, 1981). In many species of mammals (Belisle and Sainte-Marie, 1981a), these units are known as deep cortex units and some are fused to each other into deep cortex complexes and each unit is centered on the opening of an afferent lymphatic, contiguous to the peripheral cortex and bulging into the medulla of the node. In rat lymph node, the number, the size and the shape of units and/or of the complexes of a node differ to some extent according to its anatomical location (Belisle and Sainte-Marie, 1981b). The deep cortex contains specialized post capillary venules with high endothelial cells. These vessels are the portal of entry of blood-borne lymphocytes into the lymph node by migrating between the cuboidal cells of this unusual endothelium (Gartner and Hiatt, 1997; Stevens and Lowe, 1997). Some of these venules may by found in the outer cortex (Weir and Stewart, 1997).

38 In human, the parathymic lymph node has a well-developed paracortical area, which is rich in high endothelial venules (Tanegashima, Yamashita, Yamamoto and Fukunaga, 1999). The inner cortex is also known as the paracortical or subcortical zone (Weir and Stewart, 1997; Underwood, 2000; Young and Heath, 2000), juxta-medullary cortex (Ross et al., 1995) or even as the thymus-dependent zone that is occupied primarily by T-lymphocytes (Ross et al., 1995; Roitt, 1997; Tizard, 2000). In the pig, the peripheral tissue nearest the nodules contains numerous lymphoblasts and plasma cells. This is another evidence that the lymph nodes of the pig function in a similar way as in other mammals and this is propably the thymus-dependent zone (Dellmann and Brown, 1981). The inner cortex also contains many antigen-presenting cells, which are called interdigitating cells (Weir and Stewart, 1997; Underwood, 2000). The latter author added that these cells possess abundant cytoplasm with complex membrane profiles, which interdigitate with the surrounding T-cells. The paracortex area exhibited a slight but gradual reduction in size with advancing age (Luscieti et al., 1980).

I.2.A.2.B.The Medulla The cortex, in some nodes, may surround the medulla completely, but in others, the medullary tissue may border the capsule directly for long distances (Fawcett, 1994). The arrangement of dense lymphatic tissue, sinuses and trabeculae in the medulla is similar to that found in the cortex (Leeson and Leeson, 1970) but it is much less organized than the cortex (Dellmann and Brown, 1981). The medulla consists of many lymphatic vessels, medullary sinuses, lymphocytes, macrophages and plasma cells that occupy the interstics of a rich network of reticular fibres and associated reticular cells (Banks, 1993; Fawcett, 1994).

39 In the pig, the medullary cords and related aggregates of cells are located at the periphery of the node (Banks, 1993). In domestic pigs, hippopotamuses, rhinoceroses and dolphins the medulla may be shared by adjacent nodules and have very few sinuses but it consists of an evenly dense reticulum of cells. Thus the medulla is relatively impermeable to cells moving through in the lymph (Tizard, 2000). In human, the medullary area exhibits a slight but gradual reduction with advancing age (Luscieti et al., 1980). The nodes in the abdominal cavity are especially rich in medullary substance (Fawcett, 1994). Cervical lymph nodes have separate medullae (Gadre, Briner, and O’leary, 1994). In the camel, the cells of the medullary cords are lymphocytes, plasma cells, erythrocytes and occasionally macrophages, granulocytes and monocytes (Sharfee, 1989).

I.2.A.3.Lymph Circulation The circulaion of lymph through a lymph node involves afferent lymphatic vessels, a system of lymph sinuses within the node and efferent lymphatic vessels (Fawcett, 1994).

I.2.A.3.A. Afferent Lymphatic Vessels In most mammals, as the afferent lymphatic vessels approach the node they divide into several small branches that enter the node at multiple sites on its convex surface in horses (Nikles and Heath, 1992), dogs (Belz and Heath, 1995a) and human (Young and Heath, 2000). Several afferent vessels pierce the capsule on the convex side of the human lymph node and open into a system of lymph sinuses (Kessel, 1998; Rizzo, 2001). In the cat (Sugimura, 1962) and human (Pupyshev, 1989; Fawcett, 1994) the afferent vessels traverse the capsule obliquely. The afferent vessels are provided with valves with the free edge of the cusps facing toward the node to ensure unidirectional flow to the node (Fawcett, 1994; Junqueira et al., 1998). In germ-free piglets, the lymphatic vessels containing valves

40 are seen in the larger trabeculae and these open into the subcapsular sinuses (Andreson, 1972). In human, the afferent vessels in the capsule make peculiar broom-like formation, and is named terminal arborization of afferent lymphatic vessels come across the nodal capsule, with numerous holes. Their walls contain myocytes (Pupyshev, 1989). In the popliteal lymph node of the mouse, there are extranodal communications between afferent and efferent lymphatic vessels allowing some lymph to bypass the node (Kowala and Schoefl, 1986). In camels, there are large lymphatic vessels in the capsule characterized by the presence of valves and are directed toward the node (Osman, 1988; Abdel- Magied et al., 2001).

I.2.A.3.B.The System of the Lymph Sinuses Each node contains a tortuous system of irregular channels, the sinuses, within the lymphoid tissue (Leeson and Leeson, 1970). Afferent vessels enter the marginal or subcapsular sinuses, which separate the capsule from the cortical parenchyma. From the marginal sinuses, lymph flows into the cortical or intermediate sinuses that lie between the lymph nodules. Cortical sinuses are continuous with medullary sinuses, which are interposed between medullary trabeculae and medullary cords and continue into the efferent lymphatic vessels in sheep (Lowden and Heath, 1993) and dogs (Belz and Heath, 1995a). In cats, Sugimura (1962) found other sinuses called the reticular fibreless sinuses, which are situated at the corticomedullary junction. A layer of flat endothelial cells lines the wall of these sinuses without being crossed by the ordinary reticular cells. From the subcapsular sinuses the lymph may follow one of two possible routes to the efferent lymphatic vessels. It either circulates within the subcapsular sinuses and enters directly into the efferent vessels, or circulates through the trabecular sinuses, percolates through the cortex and medulla into the medullary sinuses and finally to the efferent lymphatic vessels (Dellmann and Brown, 1981). 41 In sheep, lymph enters the popliteal node either through terminal afferent lymphatics which pass within the trabeculae to the medullary sinuses or from the subcapsular sinuses traverses trabecular sinuses and/or a network of tubular sinuses in the cortex before entering the medullary sinuses (Heath, Kerlin and Spalding, 1986). Heath and Spalding (1987) added that tubular sinuses are often associated with blood vessels, especially in the deep cortex and they appear to be important in the transport of lymphocytes. In the horse, the sinus network is more extensive than in other species (Heath and Perkins, 1989). The terminal branches of the afferent lymphatics are continuous with the subcapsular and trabecular sinuses and pass to the cortex by four types of sinuses: trabecular sinuses, cortical tubular sinuses, tubule-like sinuses with a network of stellate cell processes and sinuses between cortical cords. The lymph passes through the medulla by sinuses both within and between medullary cords to efferent lymphatics by three types: those between medullary cords, those within the subcapsular sinus overlying medullary or cortical cords and those within the trabeculae (Nikles and Heath, 1992). In the pig, flow of lymph is the reverse of other domestic species. It enters at the hilus and emerges at the capsule (Banks, 1993). Dellmann and Brown (1981) and Spalding and Heath (1989b) found that the afferent lymphatic vessels enter the capsule at one or more site and penetrate deep into the central cortex as a paratrabecular lymph sinus and to the medulla at the periphery where they converge and form several efferent vessels. A similar result is found in domestic pigs, hippopotamuses, rhinoceroses and dolphins (Tizard, 2000). The medullary sinuses form a network of branching and anastomosing channels between the medullary cords (Dellmann and Brown, 1981; Fawcett, 1994). They are confluent with the marginal sinus at the hilus where it penetrates the capsule to join the efferent lymphatic (Fawcett, 1994). The sinuses are lined by endothelial cells that form a continuous lining toward the capsule and trabeculae, but the endothelium is discontinous toward the parenchyma of the node (Dellmann and Brown, 1981; Spalding and Heath, 1989b).

42 The lumina of the sinuses are traversed by a dense network of interconnected reticular cells attached to the sinus walls through numerous slender processes as a baffle to slow lymph flow within the sinuses and to facilitate antigen- cell interaction and the phagocytic activities of the macrophages (Dellmann and Brown, 1981; Roitt, 1997). In addition to lymph, sinuses contain lymphocytes and macrophages (Dellmann and Brown, 1981; Cormack, 1997). Because the macrophages are in close proximity to the sinus walls, it is difficult to separate them form endothelial and reticular cells in the light microscope (Koss, 1992). Macrophages are present throughout the node, many being found along the sinuses especially in the medulla. Most of the plasma cells are present in the medullary sinuses that are found between the medullary cords (Weir and Stewart, 1997). In rats, nodal mast cells are few in young animals, occurring mostly in medullay sinuses. Aging is often accompanied by a moderate increase of nodal mast cells (Sainte-Marie and Peng, 1990). In the camel, the subcapsular and trabecular sinuses are lined with a continuous layer of endothelial cells and basal laminae on the trabecular and capsular sides. These sinuses are traversed by reticular cells and reticular fibres and contain lymphocytes, macrophages and, in some cases, erythrocytes (Osman, 1988; Sharfee, 1989). The subcapsular sinuses are confluent with the paratrabecular sinuses (Abdel-Magied et al., 2001). The marginal and paratrabecular sinuses are prominent in the secondary mixed nodes (Sharfee, 1989). The sinuses that are found in the parenchyma are wide and lined with endothelial cells (Osman, 1988). The medullary sinuses are lined by endothelial cells and contain mainly macrophages, lymphocytes, plus few erythrocytes, which are mainly attached to or engulfed by the macrophages (Sharfee, 1989). Lymphatics and septal veins often extend into the diffuse lymphoid tissues forming networks of small sinuses. The endothelial lining of these sinuses is often discontinuous. Neumerous erythrocytes are present within or around these sinuses (Abdel-Magied et al., 2001).

43 I.2.A.3.C.The Efferent Lymphatic Vessels The efferent vessels are fewer in number and wider than the afferent vessels. They leave the node at the hilus and they are provided by valves directed away from the hilus (Fawcett, 1994; Kessel, 1998). In sheep, lymph leaves the medulla through up to 100 or more initial efferent lymphatics (Heath and Spalding, 1987). In the pig, the efferent vessels leave the node at the E-type hilus which is located between the nodular units and convex surface (Hoshi et al., 1986) . In superficial inguinal lymph nodes, the lymph flows from medullary sinuses to collecting ducts, which lack valves, and then to efferent lymphatic (Heath and Spalding, 1987). In the camel, there are in the hilus of the node large lymphatic vessels, which contain valves directed away from the node (Osman, 1988).

I.2.A.4.The Blood Circulation The arteries enter the lymph node at the hilus. The larger arterial branches initially run within the trabeculae to the capsule, whereas others enter the medullary cords and supply their capillary network. Continuing along the medullary cords, the arteries reach the cortex where they supply capillary plexuses of the diffuse lymphoid tissue and surround the germinal centres. Special postcapillary venules with low cuboidal endothelium, termed high endothelial vessels, arise from these capillary plexuses and course through the deep cortex to enter the medullary cords. There, they are continuous with small venules lined by squamous endothelial cells (Banks, 1993; Burkitt et al., 1997; Young and Heath, 2000). Dellmann and Brown (1981) and Fawcett (1994) agreed that there are small blood vessels that penetrate the capsule at various sites. In the dog, important segments of the tracheobronchial, paratracheal and receive their blood supply from capsular arteries, which encircle the capsule, rather than from hilar vessels (Salvador et al., 1992a). Belz and Heath (1995b) reported that wide variations occur in the arrangement of the blood vessels of the superficial lymph nodes. Some nodes have no identifiable hilus and arteries enter at different points.

44 Most nodes that receive arteries at a hilus, also receive additional vessels, some of which are derived from a network in the capsule and some of these enter the node by crossing the subcapsular sinuses. The postcapillary venules are found in the diffuse lymphoid tissue around the nodules (Unanue and Benacerraf, 1984), and those in the deep cortex always lack the muscular coat (Sugimura, 1962; Fawcett, 1994). The wall of the venule is traversed by a large number of blood-borne small lymphocytes which migrate into the parenchyma by insinuating themselves between the endothelial cells (Fawcett, 1994). In human the postcapillary venules are lined by cuboidal or columnar endothelial cells. This unusual endothelium allows lymphocytes to pass through the wall of the vessel but prevents passage of fluid from the vessel to the parenchyma (Ross et al., 1995). The high venules are known to be the sites of selective migration of lymphocytes into lymph nodes (Freemont and Jones, 1983). Dellmann and Brown (1981) and Junqueira et al. (1998) reported that the main vessels that supply the medullary cords enter the cortex where an arterial branch penetrates each lymph nodule and forms a dense capillary network. In domestic pigs, hippopotamuses, rhinoceroses and dolphins, circulating lymphocytes enter the lymph node in the conventional way through high endothelial venules. However, they leave the lymph node not through the lymphatics but migrate directly back into the blood stream through the high endothelial venules of the paracortex (Tizard, 2000). In human, vascular transformation of lymph node sinuses is uncommon and is characterized by conversion of nodal sinuses into the capillary-like channels. Most cases involve abdominal lymph nodes, whereas head and neck involvement is rare (Samet, Gilbey, Talmon and Cohen, 2001). In the camel, the blood vessels enter the nodes through the hilus and ramify in the interlobular connective tissue before penetrating the lobules through their hilus and capsule. They run through the trabeculae before entering the parenchyma (Sharfee, 1989). Arteries and veins are consistently seen in both the capsule and

45 septa. The septal arteries have smooth toutours and clearly discernible tunica media. Septal veins and lymphatics often extend into the diffuse lymphoid tissue, forming networks of small sinuses (Abdel-Magied et al., 2001). Capillaries occur throughout the node mainly in the medullary cord and in the germinal centre. Also, thin walled arterioles are present in the medullary cords. In the corticomedullary Junction the arterioles have a thick wall and are lined by cuboidal endothelial cells bulging into the lumen. Inside the dense lymphatic tissue, wide calibre venous sinuses of both low and ligh endothelial lining venules are present. These venules give branches around the lymph nodules (Sharfee, 1989). Large circumscribed cavities are found near the capsule of the node (Osman, 1988). In the medulla of some of the primary mixed nodes, these cavities are found at the periphery in the parenchyma of the node in between the medullary sinuses (Sharfee, 1989). Some times these cavities are connected with the subcapsular or paratrabecular sinuses, and they are filled with lymph, blood or a mixture of both (Osman, 1988; Sharfee, 1989). The cavities are lined with flat endothelium-like cells with pale and oval nuclei, which, in some instances, appear to form a discontinuous layer (Osman, 1988; Sharfee, 1989). These cavities are fewer in primary mixed lymph nodes than in secondary mixed ones (Sharfee, 1989).

I.2.B.The Haemolymph Nodes

46 The haemolymph nodes are found in man, ruminants and rats. They have been reported in the lumbar area (Banks, 1993), pelvic cavity and at the base of the neck of cattle (Hofirek and Groch, 1977) and near the kidneys, spleen and thymus in the rat (Abu-Hijleh and Scothorne, 1996). Structures, which were probably haemolymph nodes were first described by Gibbes (1884) in human perinephric connective tissue. They resemble lymph nodes but contain blood in their sinusoids. They are called haemolymph nodes by Robertson (1890) who described their occurrence independently. Vincent and Harrison (1897) found these nodes in many other mammals and also in some birds. There is no unanimity among authors on whether the haemolymph nodes are independent organs, or lymph nodes containing erythrocytes of unknown source in their efferent lymphatics. The haemolymph nodes are considered as hemorrhagic lymph nodes. However, there is evidence that these are separate and distinct entities (Banks, 1993). They are considered to be intermediate between a lymph node and haemal node (Turner, 1969; Leeson and Leeson, 1970; Fawcett, 1994) or between a lymph node and the spleen (Sakita, Fujino, Koshikawa, Ohmiya, Ohbayashi and Asai, 1997). Previous studies of the haemolymph nodes suggested that their structure in general is similar to lymph nodes (Andreason and Gottlieb, 1946; Nopajaroonsri, Luk and Simon, 1974; Kazeem, Reid and Scothorne, 1982; Tizard, 2000), but they have two principal features of their own: the absence of afferent lymphatics and the presence of erythrocytes within their sinuses. Nopajaroonsri et al. (1974) found very few afferent lymphatics and did not determine their regional origin and they specifically denied the presence of erythrocytes in the afferent lymphatics. According to Selye and Foglia (1939), haemolymph nodes of the rat do not contain free blood in the sinusoids under normal condition. Instead, red blood cells are extravasated into the tissues during the alarm reaction and are carried by lymphatics to the regional nodes, which are thereby converted to haemolymph nodes or iron pigment nodes. In the renal haemolymph node of albino rats, free erythrocytes were found in the subcapsular sinuses. In the intermediary and

47 medullary sinuses they were mostly attached to sinus macrophages. The efferent lymphatic contained a few erythrocytes (Kazeem et al. 1982). Castenholz and Castenholz (1996) reported that in rats the haemolymph nodes are characterized by a high content of blood cells most of them in different stages of erythrophagocytosis. Nopajaroonsri et al. (1974) suggested that the passage of erythrocytes is by diapedesis across the walls of capillaries and postcapillary venules into adjacent lymph sinuses. The direction of migration is from blood stream to node and that is the sole route of entry of erythrocytes into the sinuses. Kitagawa, Kudo and Sugimura. (1979), Lorvik, Gargiulo, Ceccarelli and Fagioli (1983) and Sakita et al. (1997) confirmed direct communication between lymphatic sinuses and blood vessels. Hogg, Reid and Scothorne (1982), Kazeem et al. (1982) and Kazeem and Scothorne (1982) agreed that the lymph in the afferent lymphatics contains numerous erythrocytes and they suggested that the erythrocytes enter the node through these vessels. In cattle, blood reached the node in an afferent artery which passes into the subcapsular sinus, and through the lymphoid tissue in many tiny capillaries into the central sinus from which it was collected by an efferent vein (Lorvik et al., 1983). The plasma cells in normal ovine haemolymph node are randomly located in the medullary cords of the nodes and show many cytoplasmic processes indicating motility and phagocytic activity (Al-Bagdadi, Seger, Titkemeyer and Archbald, 1986).

In the camel, Osman (1988) and Sharfee (1989) adopted the term mixed lymph nodes instead of haemolymph nodes. They suggested that their structure is similar to the lymph nodes but they contained numerous erythrocytes in their sinuses, circumscribed areas and the diffuse lymphoid tissue.

I.2.C. The Haemal Nodes

48 Clarkson (1891) proposed the name haemal glands as a suitable term for nodes which acompany the renal artery in some herbivora. The haemal nodes have been referred to previously as haemolymph glands, haemolymph nodes, glandulae haemolymphaticae, haemal glands, haemal lymphatic nodes, splenolymph glands and marrow lymph gland (Weller, 1938). They occur in a wide range of mammals including man, but common in ruminants especially in sheep (Clarkson, 1896; Leeson and Leeson, 1970; Rhodin, 1974; Fawcett, 1994). These nodes look much like typical lymph nodes except that they have a high content of erythrocytes and are interposed in the course of blood vessels (Lorvik et al., 1983; Gargiulo, Ceccarelli and Pedini, 1987; Fawcett, 1994; Frandson and Spurgeon, 1997). However, some investigators have described them as miniature spleens (Banks, 1993) or accessory spleens (Fawcett, 1994). A sizable artery enters, and a vein leaves, the hilus (Gargiulo et al., 1987; Fawcett, 1994). Some arteries discharge blood into the interstitial spaces, similar to the open circulation of the spleen (Rhodin, 1974). The blood reaches the subcapsular sinus via afferent arteries, then to the lymphatic parenchyma and the central sinus, and finally to an efferent vein (Lorvik et al. 1983; Gargiulo et al., 1987). The latter authors added that these efferent veins leave the organ at various points in the capsule and a large one, apparently connected with the subcapsular sinus, is present at the hilus.

The sinuses of the haemal nodes are either filled only with blood (Weller, 1938; Turner, 1969; Constantinescu et al., 1988; Fawcett, 1994), or with a mixture of lymph and a large amount of blood (Rhodin, 1974; Banks, 1993). The mixing is established by some arterial capillaries opening directly into the intercellular sinuses of these nodes (Rhodin, 1974). In adult goats haemal nodes, the medullary blood sinuses coalesce with each other and with the subcapsular sinus (Ezeasor and Singh, 1988). Thin walls and wide lumens containing inspissated lymph characterize the lymph vessels. They contrasted sharply with adjacent blood sinuses that are filled with elements of circulating blood (Ezeasor and Singh, 1990).

49 In the goat, circumferential lymphatic vessels abutt on the outer margins of the nodules and give rise to several radial lymphatics which branch and anastomose in between the medullary blood sinuses (Ezeasor and Singh, 1988). In the cortex they join radial branches from the medulla to form a large efferent lymph channel (Ezeasor and Singh, 1990). In large-sized haemal nodes, the capsule and trabeculae are composed primarily of smooth muscle intermixed with a few connective tissue fibres (Constantinescu et al., 1988). The reticulin fibres in the haemal node form a meshwork throughout most of the lymphoid tissue but are virtually absent from the germinal centres. The reticulin meshwork is condensed into a thick layer at the edge of the sinusoids (Turner, 1971) and from these strands of reticulin fibres extend into the sinusoidal lumen forming an open network to which the neumerous large phagocytic cells are attached (Turner, 1971; Ezeasor and Singh, 1988). Turner (1971) added that erythrophagocytosis is observed in the sinusoids. The reticular meshwork contains a large number of blood cells, many macrophages, lymphocytes and plasma cells (Gargiulo et al., 1987; Ezeasor and Singh, 1988).

In the camel, the haemal node is surrounded by a thin fibrous connective tissue capsule. Its outer surface is covered with adipose tissue and the trabeculae are thin and originate from the inner surface of the capsule. There is no clear distinction between cortex and medulla. The nodules have typical germinal centres, which are surrounded by a corona and contain capillaries. Afferent and efferent lymphatic vessels are found (Sharfee, 1989). Circumscribed areas, which are mainly found between the medullary cords, are filled with blood and are surrounded by a discontinuous endothelium. The medullary sinuses are surrounded by continuous endothelial cells and contain erythrocytes, which are attached to or engulfed by the macrophages. The postcapillary venules have thick walls and are filled with a large number of lymphocytes. The medullary cords contain two types of vessel, one of which is of

50 capillary size that runs very close to the sinusoids and circumscribed areas, whereas the other type is a much larger vessel with a thin endothelial wall (Sharfee, 1989).

I.3. Electron Microscopy

51 The capsule, the trabeculae and the reticular cells form the stroma of the lymph nodes (Sorenson, 1960; Rhodin, 1974). In rats, the framework supporting the lymphoid parenchyma consists of collagen fibres accompanied by cytoplasmic prolongations of fibroblasts (Luk, Nopajaroonsri and Simon, 1973). The predominant cells are the fibroblasts. Smooth muscle fibres are present in the capsule but absent in trabeculae (Rhodin, 1974). The capsule and trabeculae of the lymph nodes and haemolymph nodes of the rat lack smooth muscle fibres (Nopajroonsri et al., 1974). In the dog mesenteric lymph node, the reticular framwork of the medullary cord forms spongy meshes by anastomoses of stellate cells (Miyoshi and Shingu, 1984). In the pig lymph nodes, the medulla-like tissue consists mainly of reticular cells and strands of collagenous fibres (Hoshi, Hashimoto, Kitagawa, Kon and Kudo, 1988). In the mouse lymph node, fibroblastic reticular cells in the cortex are fusiform in shape and come into close proximity with the floor of the subcapsular sinus. In the medulla, there are irregular dendritic cells that surround vascular structures such as capillaries and high endothelial venules where they are organized in a discontinuous sheath-like fashion around the vessel wall (Crivellato and Mallardi, 1997). The reticular fibres consist of thin bundles of collagen fibrils (Rhodin, 1974; Ushiki, Ohtani and Abe, 1995). Rhodin (1974) classified the reticular fibres as special kind of fibril, based on the fact that they could be impregnated with silver. The fibres are continuous with the collagen fibrillar sheaths of blood vessels and lymphatic sinuses as well as with the fibrous capsule, thus acting as a skeleton of the lymph node (Ushiki et al., 1995). The germinal centre of the dog mesenteric lymph node contains a loose network of delicate stellate cells. Peripheral reticular cells of the nodule are thread- like, extending concentrically around the germinal centre (Miyoshi and Shingu, 1984).

52 Reticular cells resemble the fibroblast of loose connective tissue. The nucleus is usually elongated and pale and slightly irregular in outline (Movat and Fernando, 1964). The reticular cell is structurally similar to a macrophage and by virtue of its close proximity to extracellular connective tissue fibres, is a fixed macrophage. There is an abundance of lysosomes, some mitochondria, a few profiles of granular endoplasmic reticulum, free ribosomes (Rhodin, 1974) and a large Golgi complex (Movat and Fernando, 1964; Rhodin, 1974). Depending on its reactive stage, the reticular cell contains a varying number of phagosomes. Its surface is extremely irregular with long cytoplasmic processes extending for long distances (Movat and Fernando, 1964; Rhodin, 1974) to the extent that they are referred to as dendritic macrophage (Rhodin, 1974). The predominant cells within lymph nodes are the lymphocytes. They show considerable variation in size: small, medium and large lymphocytes (Rhodin, 1974). The separation between medium and small lymphocytes is arbitrary (Movat and Fernando, 1964). Interspersed between the lymphocytes are reticular cells, macrophages, plasma cells and mast cells. The nucleus of the small lymphocytes is usually round with minor shallow indentations. The heterochromatin is highly condensed into masses near the nuclear membrane, but also fills the major part of the interior of the nucleus. The cell surface is provided with occasional short and narrow microvilli. The cytoplasm contains a small number of spherical mitochondria and lysosomes (Rhodin, 1974). The cytoplasm is dominated by monoribosomes. The endoplasmic reticulum is rarely observed and the Golgi complex is small (Han, 1961; Rhodin, 1974). No Golgi apparatus has been observed in small lymphocytes in the superficial lymph nodes of the goat (Faroon, Henry and Al-Bagdadi, 1989). Medium-sized lymphocytes are generally round or oval .The nucleus may be slightly indented. There is a dense chromatin network and mostly one or two prominent nucleoli. There are more free ribosomes in medium-sized lymphocytes than in the small ones but fewer polyribosomes than in the large ones (Rhodin, 1974). A small Golgi apparatus is present. There is a great variation in the amount

53 of granular endoplasmic reticulum and mitochondria depending on the direction of differentiation (Han, 1961; Rhodin, 1974). Large lymphocytes have been referred to as stem cells, blast cells, basophilic stem cells, hemocytoblasts, lymphoblasts, plasmablasts, germinoblasts, activated reticular cells and transitional cells (Movat and Fernando, 1964). Large lymphocytes are identically round or oval cells. The nucleus is usually large and round but may have surface indentations, which are deeper than those present in small lymphocytes. The heterochromatin is concentrated to a thin rim near the nuclear membrance (Rhodin, 1974). Prominent nucleoli are very characteristic for the nucleus of large lymphocytes (Han, 1961; Movat and Fernando, 1964; Rhodin, 1974). One part of the nucleoli is generally connected to the chromatin near the nuclear membrance. The cell surface is slightly irregular with occasional short microvilli (Rhodin, 1974). The cytoplasm is occupied by ribosomes, mitochondria (Han, 1961; Movat and Fernando, 1964; Rhodin, 1974) and short profiles of granular endoplasmic reticulum whereas the Golgi apparatus is absent (Han, 1961; Rhodin, 1974). There is a small Golgi region (Movat and Fernando, 1964) and a pair of centrioles (Han, 1961). Erythrocytes, neutrophils and acidophils had been studied by Dellmann and Brown (1981), Birkitt et al. (1997) and Kessel (1998). The macrophages in wistar rat lymph nodes possess pseudopodia (Han, 1961; Luk et al., 1973). They are usually ovoid but they have villous processes at their cell borders, which interdigitate with those of adjacent cells, and a small nucleolus is usually observed (Movat and Fernando, 1964; Rhodin, 1974). Mitochondria are numerous and many are elongated. The nuclei are usually elongated and have one or more deep indentations (Rhodin, 1974) and are eccentrically placed (Han, 1961). The most characteristic features are the numerous lysosomes (Movat and Fernando, 1964) and many vesicles of variable size (Sorenson, 1960; Han, 1961; Movat and Fernando, 1964). Plasma cells are found in several locations in the medulla of haemal lymph nodes (Rhodin, 1974; Al-Bagdadi et al., 1986). They are ovoid with eccentric nuclei, which are round to ovoid and contain small dense nucleoli (Rhodin, 1974).

54 In sheep haemal lymph nodes, the nuclear heterochromatin is often clumped near the nuclear membrane (Al-Bagdadi et al., 1986) giving it the well-known “cart- wheel” appearance (Movat and Fernando, 1962). Occasionally, small processes as pseudopodia project into concavities within adjacent cells (Sorenson, 1960; Movat and Fernando, 1962; El-Bagdadi et al., 1986). The cytoplasm is occupied mainly by rough endoplasmic reticulum and most of the examined plasma cells showed Russell’s bodies, which are granular materials, found inside the cisternae of the rough endoplasmic reticulum (Al-Bagdadi et al., 1986). In the superficial lymph nodes of the goat, Russell’s bodies were not observed in plasma cells (Faroon et al., 1989). Morphological evidence of phagocytosis of erythrocytes by plasma cells was observed. Many plasma cells showed physical contact with mast cells in the form of cell junctions and some showed cytoplasmic continuity between the two cells (Al-Bagdadi et al., 1986). The lymphatic sinuses of wistar rats, namely subcapsular, cortical, paracortical and medullary sinuses, are in the form of continuous networks of sinuses lined by smooth surfaced lymphatic endothelial cells. These cells possess elongated nuclei and their cytoplasm contains a few organelles. No true valvular structures were identified in the sinuses (Luk et al., 1973). The endothelium of the subcapsular and trabecular sinuses of both the lymph nodes and haemolymph nodes of the rat lacks a basement membrance (Nopajaroonsri et al., 1971; Luk et al., 1973; Chetvertakova, 1976); it is supported by the trabeculae of the adjacent lymphoid parenchyma, and contains many small gaps (Luk et al., 1973). The sinuses are continuous and do not have gaps in their wall (Farr, Cho and De-Bruyn, 1980). In the pig, the endothelial cells, which configure the trabecular side of the peritrabecular lymph sinuses, have continuous endothelium with a basal lamina. The inner walls of the subcapsular lymph sinuses and parenchymal walls of the peritrabecular lymph sinuses are interrupted by numerous gaps (Hoshi et al., 1988; Spalding and Heath, 1989b). The trabeculae and their associated sinuses are continuous with the many interstitial spaces in diffuse lymphoid tissue (Spalding

55 and Heath, 1989b). In the pig lymph nodes, littoral cells separate the capsule from the subcapsular sinuses (Sasaki, Pabst and Rothkotter, 1994). In the mouse lymph nodes, dendritic sinus endothelial cells are located between the endothelial cells and the fibroblastic reticular cells (Crivellato and Mallardi, 1998). The small lymphocytes migrate by penetrating the junction between the endothelial cells of the high endothelial venules (Sugimura, Furuhata, kudo and Takahata, 1964; Wenk, Orlic, Reith and Rhodin, 1974; Anderson and Anderson, 1976; Sasaki et al., 1994) or by entering the endothelial cell body and traversing the cytoplasm (Marchesi and Gowans, 1964; Farr and De-Bruyn, 1975; Cho and De-Bruyn, 1979). After the endothelial cell has been penetrated, the lymphocytes enter the intercellular spaces (Farr and De-Bruyn, 1975). Migrating lymphocytes cross the lymphatic sinus wall by making a temporary migration pore (Farr et al., 1980). The unusual cells bridging the adluminal wall of the high endothelial venule are named intravascular bridging cells (Sasaki et al., 1994). The lymphatic sinuses of the wistar rat haemolymph and lymph nodes contain a varying number of macrophages and erythrocytes, and also a large number of erythrocytes in the lymphoid parenchyma of the haemolymph nodes (Luk et al., 1973). Erythrocytes are also present in popliteal lymph nodes of white rabbits (Sorenson, 1960). Andreason and Gottlieb (1946) suggested that erythrocytes reach the haemolymph node by reflux flow through the efferent lymphatics, which have a connection with adjacent veins. Turner (1969) and Rhodin (1974) are of the opinion that erythrocytes enter the sinuses by direct connection between capillaries and sinuses. The most likely route of entry of erythrocytes to sinuses is by crossing the wall of postcapillary venules and capillaries and then through gaps in the wall of the sinuses (Nopajaroonsri et al., 1974). Kitagawa et al. (1979) suggested that erythrocytes migrate through the endothelium of venules into extravascular area in the nodes of goats and then some of these erythrocytes migrate through the sinuses endothelium to reach the lumen of the sinuses.

56 In the camel, lymphocytes are characterized by a round or indented nucleus, a preponderance of heterochromatin, and a central nucleolus. The cytoplasm is poor in organelles (Abdel-Magid, 1986; Sharfee, 1989; Osman et al., 1992). Reticular cells are characterized by an elongated oval or irregular nucleus. The cytoplasm is rich in organelles (Abdel-Magid, 1986; Sharfee, 1989) and some of them show elongated tapering cytoplasmic processes (Osman, 1988). Erythrocytes, neutrophils and acidophils had been studied by Osman et al. (1992) and Omer (2003). Macrophages are characterized by round nuclei, but the most characteristic feature is the abundance of heterogenous lysosomal bodies (Abdel-Magid, 1986; Sharfee, 1989) and the presence of pseudopodia, which help in phagocytosis (Osman, 1988; Osman et al., 1992). Plasma cells are characterized by round nuclei with peripheral clumps of heterochromatin and the cytoplasm is filled with rough endoplasmic reticulum (Osman, 1988; Sharfee, 1989; Osman et al., 1992). All types of the blood vessel show a continuous nonfenestrated endothelium. The erythrocytes reach the lymphatic sinuses by way of the many afferent lymphatics (Abdel-Magid, 1986; Sharfee, 1989). Although erythrocytes are found in perivascular areas, no erythrocytes are seen to cross the wall of the capillaries or postcapillary venules between endothelial cells (Osman, 1988).

I.4.Morphometry

57

Although there are some quantitive observations on the lymph nodes of some mammals and man, comprehensive morphometric data on the lymph node is reported only by Abdel-Magied et al. (2001). Cervical and of athymic nude mice were compared morphometrically with those of normal littermates .The lymph nodes of the nude mice are large and the volumes of the follicles, paracortex and medulla of the lymph nodes are all large (Maruyama, Hasegawa, Kobayashi, Tanaka and Uda, 1984). Using morphometry, the morphological changes in endothelial cells of blood vessels in the uterine lymph nodes during normal pregnancy were studied (Borodin, Sklianova and Grigor’ev, 1988). A morphometric investigation of the sinuses has been performed in the mesenteric lymph nodes of man. The width of the lumen in the medullary portion is greater than that of the cortical one (Sapin and Bartosh, 1982). A morphometrical and cytological investigations are carried out on the lymph nodes to study the regional characteristics of the structure and involutionary changes in the axillary, cervical, ileac and mesenteric lymph nodes of adult humans (Triasuchev, 1983). In the camel (Abdel-Magied et al., 2001), the parenchyma constitutes about 80% of the parotid, mandibular and lateral retropharyngeal lymph nodes and the stroma constitutes about 20% of the volume of node. Morphometric analysis of the parenchymal components have shown that lymph nodules constituted about 25%, anodular dense lymphoid tissue about 34% and diffuse lymphoid tissue about 40% where as erythrocytes constitutes less than 1% of the parenchymal volume. Morphometric analysis has shown that the percentage volume densities of the stroma and the various parenchymal components are similar in the three lymph nodes.

58

CHAPTER TWO MATERIALS AND

METHODS

CHAPTER TWO

59 MATERIALS AND METHODS II.1.Gross Anatomy II.1.1. Materials The lymph nodes (see Fig. 1) used in this study were collected from 60 camels (Camelus dromedarius) of both sexes. The age of the camels ranged between two to fifteen years. The age of the animals is determined in accordance with the criterion adopted by Wilson (1984). The samples were collected from apparently healthy animals soon after death in the slaughterhouses of Omdurman, Port Sudan and Tambul camels’ market. The specimens used were obtained during the period between 2000 and 2002. II.1.2. Methods: II.1.2.A. Topography For the position of each lymphocentre, five to ten animals were examined before the specimens were removed from the animals.

II.1.2.B. Weight The specimens were weighed after fixation in 10% formalin. The fat attached to the lymph nodes was removed first. The weight was recorded by using a normal laboratory balance and the weight of each node was calculated as the average of the weights of the same nodes in ten to twenty animals.

II.1.2.C. Gross Features and Measurements Gross features and measurements of the lymph nodes were studied in ten to twenty nodes at each location, in the fresh state and after fixation in 10% formalin. The specimens were put on flat surface, and with the use of thread, the length, width, thickness and circumference were measured. The length of the thread corresponding to each specific dimension was then measured with a ruler. The absolute length of each dimension was calculated as the mean value of the total

60 measurements for each lymph node. The fresh specimens were used for the study of the colour, lobulation, shape and the number of the lymphatic vessels.

II.1.2.D. Arterial Branches of the Mammary Lymph Node The branching of the mammary lymph node arteries was studied in corrosion casts. The mammary lymph nodes were chosen because they are easily accessible and are large in size and easily handled. Five mammary lymph nodes together with their udders were removed carefully from the carcasses and then the arteries were cut some distance from the nodes. A syringe of 50 cm³ volume was used for injection of the red Vinylite into the arteries. With a slow but firm and steady pressure, each specimen was injected with acetone before injection with Vinylite. The injection of Vinylite was stopped when the colour appeared on the surface or when backpressure was felt. The prepared specimens were then placed in water and left for about 24 hours to allow the Vinylite to harden. The specimens were then put in a glass-jar containing concentrated hydrochloric acid and allowed to stay in the acid for about 48 hours. The corroded specimens were then removed from the acid gently, placed in a drain-board and the corroded flesh was washed with a fine jet of tap water. When the cast was completely clean it was placed in a glass-container covered with 10%formalin and kept there for preservation and study (Tompsett, 1956). Blue Vinylite and yellow Vinylite were used for veins and efferent lymphatics respectively. Four specimens were injected with blue Vinylite, four specimens with yellow one and four specimens with blue and yellow together but all of them failed to give good results

II.2. Histological Study For histological study, ten to twenty lymph nodes were collected from each lymphocentre and five haemal nodes from both sexes of different age. The whole lymph nodes were removed within five to thirty minutes after slaughtering the animals, and then examined grossly to detect any abnormalities and samples were only taken from the apparently normal ones. Small slices of tissue (about 5 mm.

61 thick and 1 cm. long) were taken from different parts of the cortex, hilus and medulla of some lobes of the large lymph nodes, or longitudinal or cross section of the whole small lymph nodes. Slices of tissue were fixed by immersion in different fixatives. The fixatives used were Bouin’s fluid, Zenker’s formol and 10% formalin (Culling, 1974). Zenker’s formol was found to be the best fixative for the camel lymph nodes (picric acid causes haemolysis of red blood cells). The tissue blooks were immersed in Zenker’s formol for eighteen hours. After fixation the specimens were washed in running tap water over night to remove the excess dichromate of the zenker formol. The samples were dehydrated in ascending grades of ethanol (70%, 90% and absolute alcohol, two hours for each change). The specimens were cleared in xyline or chloroform and were then transferred to the first change of molten paraffin (mp.55-60 c°) in an embedding oven for three changes, one hour for each change. The samples were blocked in paraffin wax. The blocks were trimmed and thin sections, 5-7µm thick, were cut on a rotary microtome and mounted on clean glass slides (Culling, 1974). Sections were stained with hematoxyline and eosin (H&E) for general histology (Culling, 1974). The mercuric chloride precipitates were removed by the use of alcoholic iodine (0.5% iodine in 80% alcohol) or lugol’s iodine and 3% sodium thiosulphate (Culling, 1974). Special stains were used for the study of the following components: 1-Masson’s trichrome stain was used for the differentiation of connective tissue and smooth muscle fibres (Culling, 1974). 2-Van Gieson’s stain was used to demonstrate collagen fibres (Drury and Wallington, 1980). 3-Verhoeff’s, Orcein’s and Gomori’s aldehyde fuchsin stains were used for the demomstration of elastic fibres (Drury and Wallington, 1980; Bancroft and Stevens, 1996). 4-Gomori’s silver impregnation technique to demonstrate reticular fibres (collagen type III) (Drury and Wallington, 1980; Bancroft and Stevens, 1996) .

62 5-The periodic acid-Schiff’s (PAS) technique was used for the demonstration of macrophoges (Bancroft and Stevens, 1996). 6-Gomori’s aldehyde fuchsin stain and Csaba’s alcian blue safranin method were used for the identificaton of mast cells (Drury and Wallington, 1980; Bancroft and Stevens, 1996). 7-Mayer’s hematoxyline and eosin was used for the demonstration of plasma cells (Bancroft and Stevens, 1996).

II.3. Technique for the Transmission Electron Microscope Samples for ultrastructure were taken from three apparently healthy adult camels. Small pieces of tissue were taken from the parotid and mammary lymph nodes as soon as possible after death of animals. The pieces were taken from different parts of the nodes including the reddish areas. These two nodes were chosen because they could be easily removed immediately after death of the animal. The specimens were fixed with immersion in 2.5% gluteraldehyde in 0.1M sodium cacodylate buffer pH 7.4 for two weeks (Glauert, 1974). • The fixed tissue was washed in 0.2 M cacodylate buffer. • The blocks were treated with 2%M osmium tetroxide for two hours. • Uranyl acetate in 0.69% malic acid for one hour. • Dehydration in ascending gradates of alcohol. • Cleared in propylene oxide, and embedded in TAAB resin. • Semi-thin sections were cut using a Reichert ultra-microtome. • Stained with buffered toluidine blue and the desired areas were chosen. • Ultra-thin sections were cut and mounted on uncoated copper grids.

• Ultra-thin sections were stained with lead citrate and uranyl acetate, and examined in Hitachi H-600 electron microscope. II.4. Morphometric Study

63 For this study, six normal mammary lymph nodes of three adult camels were used (three right and three left). The mammary lymph node was chosen because it could be taken away in a very short time after death of the animal and due to its large size. The specimens were removed as soon as possible after the animals were slaughtered. Water displacement technique (Aherne and Dunnil, 1982) was used for determination of the volume of the whole lymph nodes. For each specimen, the process of volume measurement was recorded three times and then the average volume as the mean value was calculated. Each lymph node was sliced into five parts of approximately equal size. One block from each part was taken with dimensions of 3 cm. in length, 2cm. in width and 5mm.in thickness. A total of five blocks per lymph node were chosen. These blocks were fixed in Zenker’s formol solution for 18 hours, processed by routine histological techniques and embedded in paraffin wax. Serial sections, 7µ thick, were cut from each block. The sections were treated with alcoholic iodine and sodium thiosulphate. This treatment was necessary for the removal of the mercuric precipitate of the Zenker’s formol fixative. The sections were stained with Masson’s trichrome. The best section from each block was selected for morphometric analysis. A total of 30 sections from 6 lymph nodes were studied. Morphometric analysis was carried out at the light microscopic level. The point counting technique of Weible (1963) and Hally (1964) was used in this study. A point counting grid of 100 points, fitted with X 12.5 eyepiece was used to analyse the sections for the determination of the volume densities of the main components of the lymph node. These components included connective tissue of the capsule and trabeculae, germinal centre, and corona, which constituted the lymph nodule, diffuse lymphoid tissue, blood and lymph vessels, sinuses and cirumscribed areas. Each section was entirely analysed field-by-field giving a range of 30-66 fields per section. The absolute volumes of the components of the lymph nodes were calculated from the volume densities (Vv) of the components and the total volume (V) of the fresh lymph nodes. Thus: absolute volume of each component=VXVv.

64 The statistical analysis of the data obtained by the point counting was restricted to the calculation of the mean and standard deviation (Weible, 1963).

65

CHAPTER THREE

RESULTS

66 CHAPTER THREE RESULTS III.1.Gross Anatomy

In present study Osman (1988) and Sharfee (1989) classification of the lymph nodes of the dromedary camel is adopted. The primary mixed lymph nodes (PMLN) are the key mixed nodes of the dromedary camel and include the parotid, mandibular, dorsal and ventral superficial cervical, axillary, tuberal, popliteal, mammary, scrotal, hepatic and renal lymph nodes. The secondary mixed lymph nodes (SMLN) include the retropharyngeal, pterygoideus, deep cervical, intercostals, thoracic aortic, mediastinal, bronchial, lumbar aortic, ruminal, reticular, omasal, abomasal, pancreaticoduodenal, jejunal, caecal, and colic lymph nodes (Fig.1). The colour of the primary mixed lymph nodes in young animals was pink. With advancing age, there were irregular dark reddish patches on the surfaces of the node. These patches were clearly seen through the capsule and were more concentrated on the medial surface especially around the hilus. These patches, in older animals, fused together and the colour of the node became dark red. The colour of the secondary mixed lymph nodes was similar to that of the primary mixed lymph nodes, but the patches were by far less. Cross sections of fresh nodes showed that the dark reddish areas were peripheral and then extended inside the lobe of the node (not all lobes contained these patches). Blood and efferent lymphatic vessels were seen at the hilus. The afferent lymphatic vessels divided several times before entering at multiple points on the surface of the node within a shallow groove but some of them were found within a deep invagination. Both size and weight were seen to increase with age. III.1.1.The Lymph Nodes of the Head The lymph nodes of the head region were grouped into three centres: parotid, mandibular and retropharyngeal lymphocentres.

67 III.1.1.A. The Parotid Lymphocentre The parotid lymphocentre consisted only of the parotid lymph node.

III.1.1.A.1. The Parotid Lymph Nodes The parotid lymph nodes consisted of a pair of superficial lymph nodes, one on each side. The parotid lymph node was embedded in the dorsocranial border of the parotid salivary gland except the cranial part of the node, which was attached to the masseter muscle, 3-3.5 cm. immediately below the base of the ear. The subcutaneous muscle of the face and the skin covered it laterally. The medial surface of the node was in close contact dorsally with the masseter artery and ventrally with the facial nerve. The hilus was located caudoventrally at the medial surface of the node (Fig.2). The shape of the parotid node in young animals was either oval or elongated (Figs.4 and 5). The lateral surface was flat whereas the medial one was convex. The surfaces of the node were smooth except at the hilus where there were many small lobes that were not separated from the main node. The shape of the node started to change with advancing age (Fig.4) and there were many differences between right and left nodes. In the right node, a fissure extended from the hilus dividing the ventral half of the node into two lobes: rostral and caudal. The rostral lobe was longer than the caudal one (Fig.5). With advancing age, the fissure became deeper and the node became U-shaped. In some specimens the left node had three surfaces. The size and weight of the parotid lymph node are shown in Table (1).

III.1.1.B. The Mandibular Lymphocentre The mandibular lymphocentre included the mandibular and pterygoid lymph nodes.

III.1.1.B.1. The Mandibular Lymph Nodes The mandibular lymph nodes were two in number, one on each side. They were situated in a depression at the angle of the mandible. The caudal part rested

68 on the bifurcation of the linguofacial vein –the lingual vein medially and the facial vein laterally– at the level of the free end of the thyrohyoid bone (Fig. 2). The lingual vein may be located in a groove between the lobes (at the hilus). The mandibular lymph nodes were covered laterally and dorsally by pterygoideus medialis muscle, medially by omohyoideus muscle and venterally by subcutaneous muscle (cutaneus faciei). In older camels, the caudal part of the node was covered, in part, by the ventral part of the submandibular salivary gland. In young animals, the lymph nodes were oval in outline when fresh, but when the lymph nodes were fixed in 10%formalin they appeared to have three surfaces: ventral, medial and lateral. The ventral surface was convex while the medial and lateral surfaces were concave, although in some animals the lateral surface was convex. The hilus was commonly located at the caudal half of the medial surface but sometimes at the centre of the same surface. The lobulation was clear in all surfaces of the node especially around the hilus (Fig.2). The shape started to change with advancing age, with many differences between the right and left node. The left node was flat while the three surfaces were still clearly seen in the right node. The lobulation became more evident in some nodes to the extent that some lobes were completely separated from the main node and connected only by connective tissue. The size and weight of the right mandibular lymph node were greater than those of the left one. The average dimensions of the mandibular lymph node are shown in Table (1).

III.1.1.B.2. The Pterygoid Lymph Node This inconstant node was only demonstrated in two out of ten heads being examined. It was embedded in fat just caudal to the maxillary tuberosity and in close contact with the dorsal part of the lateral face of the medial pterygoid muscle medially and with the medial surface of the mandible laterally. It was oval in shape and flat and the colour was pink. It had two surfaces: medial and lateral surfaces. The hilus was located in the medial surface.

69 III.1.1.C. The Retropharyngeal Lymphocentre The retropharyngeal lymphocentre consisted of only the medial retropharyngeal lymph nodes (the lateral retropharyngeal lymph nodes were absent). III.1.1.C.1. The Medial Retropharyngeal Lymph Nodes The medial retropharyngeal lymph nodes consisted of two lymph nodes one on each side of the pharynx. Each node was located in the neck ventromedial to the wing of the atlas. It had two surfaces: medial or pharyngeal, and lateral surfaces. The passage of the cranial part of the common carotid artery and the vagus nerve formed an oblique groove on the medial surface of the node. The remainder of the medial suface rested on the thyropharyngeal muscle. The ventrocaudal part of the medial surface of the submandibular salivary gland covered the lateral surface of the node except the caudal part, which was coverd by the external jugular vein or the maxillary vein. In young animals, the medial retropharyngeal lymph node was irregular in shape, elongated or quadrate, in which the rostral part was wider than the caudal one. The lateral surface was flat and incomplete lobulation was seen at the medial surface around the impression of the common carotid artery and vagus nerve. There was a separate lobe located at the caudal or caudomedial part of the node. In more than 50% of the animals, the rostral part of the node was divided, in part, by a fissure into two small parts. In old animals, the shape was commonly elongated and both the lateral and medial surfaces were more lobulated than those of young animals. The size and weight of the medial retropharyngeal lymph nodes are shown in Table (1).

III.1.2. The Cervical Lymph Nodes The cervical lymph nodes were classified into superficial cervical lymphocentre and deep cervical lymphocentre. III.1.2.A.The Superficial Cervical Lymphocentre

70 The superficial cervical lymphocentre consisted of two lymph nodes, the dorsal superficial and ventral superficial cervical lymph nodes.

III.1.2.A.1. The Dorsal Superficial Cervical Lymph Nodes The dorsal superficial cervical lymph nodes were found on both sides of the neck, they were relatively large elongated lymph nodes. Each node was situated craniodorsal to the shoulder joint. It was related medially to the lateral surface of the serratus ventral cervicis and scalenus medius muscles, whereas laterally it was covered by the medial surface of the cleidomastoideus muscle. The node was embedded in a large amount of adipose tissue, which separated the node from the muscles. The dorsal superficial cervical lymph node had three surfaces and the ventral surface was more convex than the two dorsal ones. These three surfaces were not clear in young animals. The hilus was located in the angle between the two dorsal surfaces. The two ends of the node tapered sharply with advancing age. The lobulation was clear in all surfaces of the node especially around the hilus.

III.1.2.A.2. The Ventral Superficial Cervical Lymph Nodes The ventral superficial cervical lymph nodes were represened on both sides of the neck, by a relatively one large globular, and some times oval, lymph node and they were palpable. Each node was situated in the caudal and ventral part of the neck, cranial to the shoulder joint and between the superficial pectoral and the sternocephalic muscles. It was related to the superficial cervical artery and sometimes to the external thoracic vein and the phrenic nerve. It was embedded in a large amount of adipose tissue, which separated the node from the muscles. The skin covered them ventrally. An elongated fissure on the deep face of the node represented the hilus. The lobulation was clear in all surfaces of the node especially around the hilus.

71 The size and weight of the dorsal and ventral superficial cervical lymph nodes are shown in Table (1).

III.1.2.B. The Deep Cervical Lymphocentre The deep cervical lymphocentre comprised a number of nodes scattered along the course of the common carotid artery and the vagus nerve in close relation to the cervical portion of the trachea. A clear asymmetry in their position, size and number was noted; the number was greater on the left than on the right side. These nodes were grouped into cranial, middle and caudal groups. III.1.2.B.1. The Cranial Deep Cervical Lymph Nodes The cranial deep cervical lymph nodes were located on both sides of the trachea just caudal to the larynx at different positions and related to the thyroid gland. They consisted of 2-3 lymph nodes of different size. The first node was located craniodorsal to the medial surface of the thyroid gland by which it was covered. The right node was flat and oval or elongated in shape. It rested on and attached to the cricopharyngeal muscle and extended to the first tracheal ring. The left node was the largest one of the cranial deep cervical lymph nodes. It was oval or irregular in shape, and was lobulated and contained a separate lobe that was located cranioventral to the main node. It rested on the first to third tracheal rings and was covered by the medial surface of the left lobe of the thyroid gland .The hilus was in a fissure located in the caudal part of the node. The second node was oval or elongated in shape and located caudoventral to the thyroid gland between the ventral part of the 4-5 tracheal rings in the right side and 8-9 tracheal rings in the left side. It was covered laterally by the common

72

carotid artery and the vagus nerve. The right node was also related medially to the isthmus or the caudal part of the right lobe of the thyroid gland and ventrally to the sternothyroideus muscle. The right second node was the largest node in the right side. The left node was more flat than the right one. In the right side, there was a third small node located mediocaudodorsal to the right lobe of the thyroid gland. It rested on the dorsal surfaces of the fourth

73 and fifth tracheal rings and was covered by the right lobe of the thyroid gland. It was also related to the oesophagus. A comparison between the average dimensions of the cranial deep cervical lymph nodes is shown in Table (2).

Table (2): showing a comparison between the average dimensions of the cranial deep cervical lymph nodes. R.F.N. L.F.N. R.S.N. L.S.N. Length /cm. 2.3-3.5 5.5-7.0 3.5-4.2 2.0-2.5 Width /cm. 1.3-2.0 1.5-2.2 0.7-1.1 0.5-0.9 Thickness /cm. 0.3-0.5 0.2-0.4 0.3-0.5 0.1-0.3 Circumference/cm. 2.5-3.5 2.7-3.1 2.0-2.7 1.3-1.9

R.F.N.=Right First Node. L.F.N.= Left First Node. R.S.N.= Right Second Node. L.S.N.= Left Second Node.

III.1.2.B.2. The Middle Deep Cervical Lymph Nodes The middle deep cervical lymph nodes were situated along the cervical trachea. The right node was usually absent, but when present, it was flat and elongated and located between the 15-16 tracheal rings medially and the common carotid artery and vagus nerve laterally. The hilus was located at the caudoventral surface of the node (Fig. 6). The left nodes were small and elongated and arranged in linear series extending along the ventrolateral aspect of the trachea from the level of the 13-42 tracheal rings. At the 13-14, 15-16 and 18-19 tracheal rings, the nodes were covered by the common carotid artery and at the 35-36, 37-38 and 41-42 tracheal rings they were covered by the oesophagus and the fascia that surrounded the

74 sternothyroideus muscle. The node that was located at the level of 15-16 tracheal rings showed darker reddish areas than the others.

III.1.2.B.3. The Caudal Deep Cervical Lymph Nodes The caudal deep cervical lymph nodes were located at the thoracic inlet just cranial to the first rib. They were flat (some times lobulated) and oval or elongated lymph nodes. They extended from the level of the 45-47 tracheal rings on the right side and 47-49 tracheal rings on the left side. They are covered by the oesophygus, common carotid artery, vagus nerve and the fascia laterally, and the trachea medially. The left node was larger and more lobulated than the right one. The caudal deep cervical lymph nodes showed more dark areas than the others groups. A comparison between the average dimensions of the right and left middle and caudal deep cervical lymph nodes is shown in Table (3). Table (3): Showing a comparison between the average dimensions of the right and left middle and caudal deep cervical lymph nodes. The node Length /cm. Width /cm. Circumference/cm. R. M. D. C. 2.0-2.5 0.3-0.7 1.2-1.5 L. M. D. C. 1.2-1.6 0.7-1.0 1.7-2.2 R. C. D. C. 3.2-3.5 1.0-1.5 2.5-2.9 L. C. D. C. 2.7-2.9 0.9-1.2 1.5-2.0

R. M. D. C. = Right Middle Deep Cervical. L. M. D. C. = Left Middle Deep Cervical. R. C. D. C. = Right Caudal Deep Cervical. L. C. D. C. = Left Caudal Deep Cervical. III.1.3.Some Lymphocentres and Lymph Nodes of The Thorax III.1.3.A. The Intercostal Nodes The intercostal nodes were inconstant and bilaterally scattered near the costoverteberal articulation, dorsal to the sympathetic trunk. They were located in contact with the longus colli muscle. These nodes were oval in shape with small

75 hilus on the deep face. They were of different sizes and embedded in adipose tissue and covered by the costal pleura. The first node was the smallest of the series. Not all the intercostal spaces contained lymph nodes, and exceptionally 2-3 nodes occurred in the 4th-6th intercostal spaces. They were related to the intercostal vessels.

III.1.3.B. The Thoracic Aortic Nodes These were in the form of a series of 3-4 small nodes embedded in adipose tissue and located along the dorsolateral border of the thoracic aorta and ventral to the sympathetic trunk. They were scattered at the level of the 7th-11th ribs on the lateral surface of the thoracic vertebral bodies. They were oval in shape and of different sizes.

III.1.3.C. The Mediastinal Lymphocentre The mediastinal lymphocentre consisted of a number of widely dispersed nodes, placed between the two lamellae of the mediastinal pleura. They were the largest accumulation of nodes in the thorax. For the sake of simplicity, they were classified according to their position into three main groups in the mediastinum, namely cranial, middle and caudal mediastinal lymph nodes.

III.1.3.C.1. The Cranial Mediastinal Lymph Nodes The cranial mediastinal nodes consisted of a number of nodes of different sizes scattered in the cranial medistinum. They were embedded in adipose tissue. They consisted of the following nodes: • Large oval or elongated node measured 7.5-8.5 cm. in length, 1.2-1.5 cm. in width, 1.0-1.2 cm. in thickness 3.5-4.0 cm. in circumference, interposed between the trachea and longus colli muscle. This node contained more dark areas than the others. • A group of 3-4 nodes deeply situated between the trachea and the cranial vena cava. They were located on the termination of the

76 subclavian artery and were separated from it by adipose tissue. They were related to the vagus nerve. The largest node was oval in shape and measured 4.5-5.0 cm. in length, 2.0-2.5 cm. in width and 0.4-0.6 cm. in thickness. With advancing age, the remainder small nodes were fused together to form one globular node. • A small node was found in the angle between the costocervical and subclavian veins.

III.1.3.C.2. The Middle Mediastinal Lymph Nodes The middle mediastinal lymph nodes were placed dorsal to the base of the heart and they were divided into the following sets: • A small node was located in the angle formed by the confluence of the right azygos vein and cranial vena cava. It was related to the vagus nerve. • 1-2 elongated nodes were aggregated caudal and lateral to the right azygos vein and caudal to the aortic arch. They were related to the thoracic oesophagus. They were embedded in adipose tissue .The large node was elongated in shape and measured 3.2-3.8 cm. in length, 1.0-1.5 cm. in width and 0.2-0.4 cm. in thickness.

III.1.3.C.3. The Caudal Mediastinal Lymph Nodes The caudal mediastinal lymph nodes were located in the caudal mediastinum caudal to the aortic arch. They were situated 1.5-3.0 cm. ventral to the aorta and 4.0-6.5 cm. dorsal to the thoracic oesophagus, embedded in adipose tissue (Fig. 3). In young animals, 2-3 nodes were found in one line and they were elongated and flat. With advancing age, the cranial small nodes increased in size and fused with the third node to form one long node measuring 17.5-35.0 cm. in length. This node extended to the level of dome of the diaphragm. The width of the narrow cranial and caudal parts of the long node was about 0.5-1.2 cm. and the medial part

77 was the widest part of the node, measuring 0.9-2.5 cm. (Fig.3). These long nodes had several hiluses that were located dorsally at a groove filled with adipose tissue.

III.1.3.D. The Bronchial Lymphocentre The bronchial lymphocentre consists of the tracheobronchial lymph nodes, which were placed around the trachea and bronchi. These nodes were described according to their association with the principal segments of the tracheal bifurcation. Thus, right, left and dorsal nodes were considered.

III.1.3.D.1. The Right Tracheobronchial Lymph Node The right tracheobronchial lymph node was single and inconstant node, placed on the right face of the trachea immediately before the tracheal bifurcation. Medially it was related to the trachea and laterally to the visceral surface of the right lung.

III.1.3.D.2. The Left Tracheobronchial Lymph Node The left tracheobronchial lymph node was located on the dorsolateral aspect of the left principal bronchus and caudolateral to the aortic arch. Its base was in contact with the caudal aspect of the aortic arch. The apex was located close to the hilus of the left lung. It was embedded partially in and covered laterally by the medial face of the cranial lobe of the left lung. The remainder of the node was embedded in an adipose tissue at the base of the heart. The node was roughly triangular in outline and measured about 4.5-6.0 cm. in length, 2.2-2.8 cm. in width and 0.2-0.5 cm. in thickness.

III.1.3.D.3. The Dorsal Tracheobronchial Lymph Node The dorsal or middle tracheobronchial lymph node was large and located dorsal to the bifurcation of the trachea, in close relation to the right face of the oesophagus and abdominal aorta and laterally to the visceral surface of the right lung. In young animals it was oval in shape and became elongated with advancing

78 age. The left tracheobronchial lymph node contained more dark reddish areas than the other tracheobronchial nodes. In some specimens, one small haemal node was present at the ventral surface of the trachea 7 or 8 tracheal rings cranial to the bifurcation.

III.1.4. Some Lymphocentres and Nodes of the Abdominal and Pelvic Wall, Viscera and Hindlimb III.1.4.A. The Lumbar Lymphocentre The nodes of this centre were scattered in the sublumbar region. This centre included the lumbar aortic and renal lymph nodes. III.1.4.A.1. The Lumbar Aortic Lymph Nodes The lumbar aortic lymph nodes were scattered and embedded in the fascia and fat on the ventral aspect of the abdominal aorta and caudal vena cava and their branches at the level of the cranial half of the left kidney. They were related to the lumbar splanchnic nerve. They were usually two in number, and oval in shape. The right node was related to the caudal vena cava and the psoas minor muscle. The left node was located in the angle between the abdominal aorta and renal blood vessels and the psoas minor muscle. Their size gradually became larger with advancing age and the nodes came closer to the psoas minor muscle.

III.1.4.A.2. The Renal Lymph Nodes The renal lymph nodes could not sharply be separated from the lumbar aortic lymph nodes. They were described separately according to their proximity to the kidneys. The right renal nodes were divided into two sets .The first set was represented by 1-2 small roughly spherical flattened nodes. They were embedded in adipose tissue adjacent to the right renal hilus and were related to the right renal blood vessels. The second set consisted of two small nodes embedded in adipose tissue in the angle between the caudal vena cava and the right renal artery at the level of the caudal half of the right kidney.

79 The left renal nodes were two small, oval and flattened nodes embedded in adipose tissue in the vicinity of the left renal blood vessels at the level of the cranial half of the left kidney. The renal nodes measured about 2.7-3.7 cm. in length, 1.3-2.0 cm. in width, 0.7-0.9 cm. in thickness and 4.0-4.6 cm. in circumference.

III.1.4.B.The Superficial Inguinal Lymphocentre This centre consisted of one node situated in association with the scrotum or mammary gland, in the male and female respectively. III.1.4.B.1.The Scrotal Lymph Node The scrotal lymph node was demonstrated just under the skin of the prepubic region. They were two conglomerations of lymph nodes situated on the ventral side of the abdominal wall embedded in adipose tissue cranial and caudal to the spermatic cord. In young animals, the nodes could be easily manipulated at the neck of the spermatic cord. In older animals, the increase in the thickness of the skin and accumulation of fat makes palpation nearly impossible. The node was either elongated or crescent in shape. An elongated fissure on the deep face of the node represented the hilus. The lobulation was clear in all surfaces of the node especially around the hilus. The size of the scrotal lymph node is shown in Table (4).

III.1.4.B.2.The Mammary Lymph Nodes The mammary nodes were the largest lymph nodes in the camel. They were paired, one on each side. Each was embedded in a considerable amount of fat at the superficial ring of the inguinal canal. It was located cranial to the dorsolateral side of the mammary gland. The node was related laterally to the sartorius and tensor fasciae latae muscles and to the external pudendal artery and vein. This node was crescent in outline with the concavity facing dorsally. It showed distinct lobulations, especially the dorsal surfaces where many separate lobes were found

80 around the hilus. The hilus was elongated and found in a long groove (Figs. 8 and 9). The size and weight of the mammary lymph node are shown in Table (4). The mammary lymph node received blood from 7-10 arteries that arose either directly from the external pudendal artery or from one of its branches. The major nodal arteries entered through a fat-filled hilar groove, whereas other arteries penetrated the capsule directly. As the major nodal arteries approached the lymph node they divided into many smaller arteries and branched extensively over the node surface. Some branches penetrated directly into the lymphoid parenchyma through the inter-lobular connective tissue and then ran through trabeculae before entering the parenchyma (Fig. 7). Branches from different major nodal arteries frequently anastomosed and some of them sent small branches to adjacent fat and connective tissue. Although the mammary lymph node was large and had a lobular appearance yet it had no segmental blood supply, i.e. many arteries supplied more than one lobule (Fig. 7). Table (4): Showing a comparison between the average dimensions of the scrotal and mammary lymph nodes. Minimum Maximum Average Scrotal Mamm- Scrotal Mamm- Scrotal Mamm- ary ary ary Wight (gm.) 12.07 19.13 48.75 110.16 28.54 64.27 Length /cm. 5.70 6.70 7.40 14.70 6.57 10.25 Width /cm. 2.00 2.10 3.40 5.10 2.76 2.90 Thickness /cm. 1.70 1.90 2.50 4.60 2.07 3.02 Circumference/cm. 7.20 6.80 10.10 15.30 8.39 10.89

III.1.4.C.The Subiliac Lymph Nodes (Prefemoral) The subiliac lymph nodes were absent.

III.1.4.D. The Tuberal Lymph Nodes

81 The tuberal lymph nodes consisted of two superficial lymph nodes, one on either side at the pelvic outlet. They were embedded in adipose tissue medial to the caudal border of the sacrotuberal ligament, and lateral to the gluteus medius muscle and about 8-10 cm. from the tuber ischiadicum. They were covered by the skin and sometimes were covered partially by the ligament mentioned above. They were also related to the lateral vein of the tail (caudalis lateralis vein). They were ovoid in shape and an elongated fissure on the deep face of the node represented the hilus. The lobulation was clear in all surfaces of the node especially around the hilus. The tuberal lymph nodes measured about 4.2-5.5 cm. in length, 2.7-3.2 cm. in width, 1.3-1.9 cm. in thickness and 5.7-6.5 cm. in circumference.

III.1.4.E. The Gastric Lymph Nodes The gastric lymph nodes were represented by a large number of nodes that accompanied most of the neurovascular tree which spreaded over the different compartments of the stomach. They were mostly placed under the peritoneum or between the two layers of the omenta. They were subdivided into several groups according to their association with the different parts of the stomach:

III.1.4.E.1. The Atrial Lymph Nodes The atrial lymph nodes were absent.

III.1.4.E.2. The Right Ruminal Lymph Nodes The right ruminal nodes were located on the right face of the rumen. They were of different size and shape. They were 5-6 in number and oval, elongated or irregular nodes of about 1.6-7.0 cm. long, 1.1-2.5 cm. wide, 0.4-0.9 cm. thick and 2.5-6.0 cm. in circumference. They were embedded in adipose tissue on the dorsal aspect of the right ruminal artery along its course in the right longitudinal groove. They were lobulated and contained more reddish areas than the other gastric nodes.

82 III.1.4.E.3. The Left Ruminal Lymph Nodes The left ruminal lymph nodes were found cranial to the left longitudinal groove, in the adipose tissue of the and associated with the left ruminal vessels. They were two to three large ovoid nodes of about 2.0-3.5 cm. long, 1.2-2.5 cm. wide, 0.5-0.9 cm. thick and 3.0-4.2 cm. in circumference .Two to three smaller nodes of a pea size could also be found in this group. With advancing age, some or all of the large nodes were fused together to form one irregular node.

III.1.4.E.4. The Cranial Ruminal Lymph Nodes The cranial ruminal lymph nodes were embedded in adipose tissue and scattered in the cranial part of the ventral sac of the rumen by the side of the right ruminal artery. They were three large ovoid or globular nodes of about 1.0-3.5 cm. long, 1.0-2.5 cm. wide, 0.5-0.9 cm. thick and 2.2-35 cm. in circumference.

III.1.4.E.5. The Reticular Lymph Nodes The reticular lymph nodes were divided into two sets .The first set was represented by 10-13 nodes which were either oval, elongated, triangular or kidney- shaped and were 1.0-5.5 cm. long, 0.5-1.9 cm. wide, 0.3-1.4 cm. thick and 1.5-6.0 cm. in circumference. They were embedded in adipose tissue of the lesser omentum in the lesser curvature of the reticulum. They were scattered along the course of the ruminal artery. With advancing age, some of them fused together to form one irregular elongated node. Two to three smaller nodes of a pea size were also included in this group. The second set consisted of three small oval nodes embedded in adipose tissue in the greater curvature of the reticulum and each one measured not more than 1 cm..

III.1.4.E.6. The Omasal Lymph Nodes The omasal lymph nodes were 12-15 in number, scattered in the lesser and greater omentum of the omasum. They were arranged in two sets.

83 The greater number of the nodes constituted the dorsal set, which was situated on the greater omentum of the omasum. These nodes were 10-12 in number and were spherical, oval, elongated or heart-shaped of about 1-4.8 cm. long, 0.4-1.8 cm. wide, 0.4-0.9 cm. thick and 1.0-4.2 cm. in circumference. They were grouped around the left gastric artery, especially those located cranially. They were embedded in adipose tissue of the greater omentum, and because of their small size, especially those located caudally, they could escape notice. Two to three additional smaller nodes of a pea size were found in the vicinity. The ventral set, two to three nodes, was aggregated and embedded in adipose tissue in the cranial part of the lesser omentum of the omasum. They were oval or elongated in shape and about 1.7-6.0 cm. long, 0.7-2.5 cm. wide, 0.5-0.9 cm. thick and 2.5-5.0 cm. in circumference .Two to three smaller nodes of a pea size were also found in the vicinity. The dorsal set was more lobulated and contained more reddish areas than the ventral one.

III.1.4.E.7. The Abomasal Lymph Nodes The abomasal lymph nodes consisted of one or two large globular nodes embedded in adipose tissue of the greater omentum and two to three small ovoid nodes embedded in adipose tissue of the lesser omentum. They were about 2.9-3.5 cm. long, 1.9-2.8 cm. wide, 0.4-1.6 cm. thick and 4.3-5.7 cm. in circumference.

III.2. Histology III.2.I. The Lymph Nodes

84 The lymph nodes were surrounded by a connective tissue capsule (Figs. 10, 12 and 13). Thick trabeculae passed from the capsule to the substance of the node, dividing the node into many complete, or incomplete, lobes (Fig. 11). From the inner surface of the capsule and the thick trabeculae originated thin trabeculae that passed into the parenchyma dividing the lobes into many complete or incomplete lobules (Fig. 10). The parenchyma of the lobules consisted of a cortex and medulla. The cortex was either organized in the form of lymph nodules or diffuse lymphoid tissue. In young animals, a greater portion of the primary mixed lymph nodes and the whole secondary mixed lymph nodes were typical lymph nodes, but some parts of the primary mixed lymph nodes revealed the presence of erythrocytes within the tissue spaces, so that the organ was at least partially a mixed node (Fig. 11). In old animals, approximately all the primary mixed lymph nodes and some of the secondary mixed lymph nodes revealed the presence of erythrocytes.

III.2.I.1. The Capsule The lymph nodes were surrounded by a capsule of dense irregular connective tissue consisting mainly of large bundles of collagen fibres (Fig. 12) and a few elastic (Figs.13 and 32) and reticular fibres. The outer part of the capsule contained more elastic fibres than the inner one. In the outer part of the capsule, the elastic fibres were coarse and dense whereas in the inner part the fibres were fine and a few in number (Fig.13). Elastic fibres were also demonstrated in large blood and lymphatic vessels of the capsule. A few reticular fibres were scattered within the capsule. The amount of the connective tissue increased with advancing age and it was more in the primary mixed lymph nodes (Fig.10) than in the secondary mixed lymph nodes (Fig.12) to form a thick and a thin capsule respectively. The capsule contained adipose tissue. The capsule also contained a sympathetic ganglion of the dorsal superficial cervical lymph node.

85 Smooth muscle fibres were only found in the tunica media of the blood vessels and between the collagen fibres of large lymphatic vessels of the capsule. Blood vessels, afferent lymphatic vessels, myelinated nerve fibres, reticular cells, large number of fibroblasts and plasma cells were observed within the capsule. The outer surface of the capsule merged with the surrounding adipose tissue (Fig.12) or loose connective tissue, whereas the inner surface was delineated by the subcapsular sinuses, which were lined by a continuous layer of endothelial cells on the capsular side of the sinus (Figs.13 and 28). A number of afferent lymphatic vessels pierced the capsule on the convex side of the node and opened in the subcapsular and cortical sinuses. The capsule was thickest at the hilus where it surrounded the efferent lymphatic vessels and blood vessels. The hilar structure varied considerably in the different groups of lymph nodes and was easily distinguishable with advancing age. The hilar depression varied in position, size and depth and was filled with a pad of fat. The simplest form of the hilus was seen in the secondary mixed lymph nodes where it extended some distance into the node, and the subcapsular sinuses were infolded at the hilus and separated the hilar intrusion from the lymphoid tissue. In the depth of the node, where the hilus was divided, the subcapsular sinuses were joined to the medullary sinuses to form the efferent lymphatic vessels. The large primary mixed lymph nodes had different hilar structure, providing adequate hilus for the large aggregation of lymphoid tissue. The main hilus was superficial and several superficial hiluses were found in elongated nodes and were extended inside the node to form thick trabeculae. Small hilar protrusions extended far into the nodular tissue and formed thin trabeculae that branched to form the cortical and medullary trabeculae of the lobule. The hilus contained a large number of nerve bundles in jejunal and pancreaticodudenal lymph nodes.

III.2.I.2. The Trabeculae

86 In the primary mixed lymph nodes, the thick trabeculae started from the hilus or the internal surface of the capsule and usually branched before ending in the capsule in another site. From the inner surface of the capsule and thick trabeculae originated a variable number of thin branching trabeculae, which passed into the lymphoid parenchyma of the lobe dividing it into many lobules (Fig. 11). These thin trabeculae were highly branched to form the cortical and medullary trabeculae. The trabeculae had the same components of the capsule but were completely surrounded by endothelial cells of the paratrabecular sinuses (Fig.15), and the elastic fibres were concentrated at the core of the trabeculae far away from the paratrabecular sinuses (Fig.14). The seconary mixed lymph nodes had poorly developed thin interrupted trabeculae, which had the same components of the capsule. Arterioles were found within these trabeculae.

III.2.I.3. The Parenchyma In the primary mixed lymph nodes, it was difficult to distinguish the cortex and medulla (Fig.16). Silver staining disclosed obvious differences between the cortical and medullary reticulum with advancing age (Figs.24 and 25). In the seconary mixed lymph nodes, there was distinct but irregular demarcation between the cortex and medulla, which became more distinct with advancing age (Fig.17). III.2.I.3.A. The Cortex In the cortex of the lobule, the lymphocytes were organized into lymph nodules and diffuse lymphoid tissue (Figs.21 and 22). III.2.I.3.A.1. The Lymph Nodules The lymphocytes formed a variable number of densely packed lymph nodules (Fig.16). There was no constant relationship between the number of the nodules and the location of the node. There was fusion of nodules, especially in the axillary and retropharyngeal lymph nodes (Fig.18). The distribution of the lymph nodules was not even in all lobes of the node. In the light diffuse lymphoid tissue,

87 the number and size of the nodules were decreased. The lymph nodules were of two types: primary and secondary nodules.

III.2.I.3.A.1.A. The Primary Lymph Nodules The primary lymph nodules appeared as discrete spherical or ovoid areas of tightly packed small lymphocytes that were devoid of germinal centres. They were found mainly in old animals and their size decreased with advancing age.

III.2.I.3.A.1.B. The Secondary Lymph Nodules The secondary nodules were located at the periphery of the lobules of the node (Fig.16). They were situated below the capsule in close association with the subcapsular sinus and on either side of the trabeculae, separated by the paratrabecular sinuses (Fig.19). The meshwork of the lymph nodules was filled with lymphocytes of different sizes. The large and medium-sized lymphocytes were found at the centre of the nodule forming a pale central area, the germinal centre, whereas small lymphocytes were often found at the periphery of the lymph nodules forming a corona (Figs.14, 16, 18 and 21). The cytoplasm of the large lymphocytes was plenty. The large and medium-sized lymphocytes had spherical or oval shape and large oval, spherical or indented euchromatic nuclei with one or two prominent nucleoli (Fig.20). Also seen in the germinal centre were monocytes, neutrophils, plasma cells, macrophages, lymphoblasts in different phases of mitotic division, fibroblasts, a small number of small lymphocytes and reticular cells. Small lymphocytes were aggregated in the form of half moons (demilunes) when the lymph nodules were located near a single trabeculum or the capsule. The demilune corona was located facing the nearby trabeculum or capsule (Figs.16 and 18). But if the lymph nodule was located between capsule and trabeculum or between two or more trabeculae, the aggregation of the small lymphocytes completely surrounded the germinal centre (Figs.16 and 37). The small lymphocytes were spherical in shape with scanty cytoplasm and darkly stained nuclei and they were usually packed together (Figs.19 and 20).

88 The nodules appeared to be less vascular than the surrounding lymphoid tissue. Capillaries from different directions entered the nodules and branched into small capillaries (Fig.21). These capillaries were supported by reticular and elastic fibres. The lymph nodules were supported by reticular fibres especially at the junction with the marginal zone and the corona. At the centre of the lymph nodules the framework consisted of scattered reticular fibres in close contact with the blood vessels (Fig.17). The elastic fibres were also found and had similar distribution to reticular fibres. In young animals, the majority of lymph nodules had a large germinal centre and a narrow corona (Figs.16 and 18). The nodules were numerous and of large size, with narrow spaces between them especially in the axillary lymph nodes. With advancing age, the germinal centres became smaller and completely surrounded by a wide corona. The nodules were few in number and small in size. The secondary lymph nodules then lacked the germinal centres and became primary lymph nodules and contained a large number of erythrocytes scattered between the small lymphocytes. The marginal zone was supported by a reticular and elastic meshwork at the periphery of the lymph nodules (Fig.17). The meshwork of the marginal zone supported a large number of lymphocytes, reticular cells, fibroblasts, a few monocytes, macrophages and plasma cells. The marginal zone was in direct continuation with the lymph nodules and there was no demonstrable line of demarcation between them.

III.2.I.3.A.2. The Diffuse Lymphoid Tissue The diffuse lymphoid tissue was in the form of dense and light lymphoid tissue (Fig.22). The stroma of the diffuse lymphoid tissue was supported by a connective tissue framework consisting mainly of a network of reticular (Fig.17), collagenous and fine elastic fibres. Smooth muscle fibres were only found in blood and large lymphatic vessels.

89 The reticular fibres and fine elastic fibres were plenty around the cortical sinuses (Fig.29), circumscribed areas and blood vessels. In the secondary mixed lymph nodes, the reticular fibres were more than in the primary mixed lymph nodes. The collagenous fibres were more in the stroma of the medulla than in the cortex. The cellular components of the cortical diffuse lymphatic tissue were lymphocytes of different size, plasma cells, fibroblasts, reticular cells, macrophages and, sometimes, erythrocytes. The diffuse lymphatic tissue contained the cortical sinuses, circumscribed areas and blood vessels (Figs.13, 31, 32 and 34). The deep cortex contained specialized post-capillary venules with high endothelial cells.

III.2.I.3.B. The Medulla The medulla was found in three forms: either surrounded completely by the cortex, or intervened through the cortex, or bordered directly the trabeculae and the hilus. It contained medullary sinuses, blood vessels and circumscribed spaces, which were lined by endothelium. The trabeculae were extensively branched, the blood vessels were plenty and the sinuses were interconnected (Figs.17, 23 and 25). The lymphocytes of the medulla were arranged in the form of cords usually known as medullary cords. Reticular cells, plasma cells, erythrocytes and sometimes macrophages, granulocytes and monocytes were also represented in the medulla. The seconary mixed lymph nodes were rich in medullary substance. With regard to the width of the medulla in relation to the cortex, no definite tendency was found with advancing age, but it became paler due to increased amount of collagen fibres. So the collagen fibres were scattered in the stroma of the medulla more than in the cortex.

III.2.I.4. The Lymph Circulation

90 The circulation of the lymph through a lymph node involved afferent lymphatic vessels, a system of lymph sinuses within the node and efferent lymphatic vessels. III.2.I.4.A. The Afferent Lymphatic Vessels Several afferent lymphatic vessels approached the node and divided into several branches that pierced the node at multiple sites of the capsule to open into the subcapsular or cortical sinuses (Figs.26, 27 and 30). Another route, the afferent lymphatics approached the thick and thin trabeculae and sent branches which opened in the paratrabecular sinuses. The afferent lymphatic vessels were lined by endothelial cells with flattened nuclei and were surrounded by subendothelial bundles of collagen fibres (Figs.26 and 27), and a few elastic and reticular fibres. A few smooth muscle fibres were located adjacent to the endothelium in the form of isolated fibres. These smooth muscle fibres, in a few instances, formed a continuous layer. The lymphatic vessels contained lymphocytes, and blood cells especially red blood corpuscles in the primary mixed lymph nodes. The afferent lymphatic vessels were provided with valves with the free edges of the cusps directed toward the node. These valves were covered by endothelium and had a core of dense connective tissue, which was devoid of smooth muscle fibres (Fig.27).

III.2.I.4.B. The Sinus System Each node contained a system of interconnected irregular channels, the sinuses, within the lymphoid tissue. The sinus system comprised three types of sinus according to their location: subcapsular and paratrabecular, cortical and medullary sinuses. In the primary mixed lymph nodes the cortical sinuses were larger than the medullary ones. The terminal branches of the afferent vessels entered the subcapsular and paratrabecular sinuses (Fig.27), which separated the capsule and trabeculae respectively from the cortical parenchyma. These sinuses opened into

91 circumscribed areas, which were sometimes found beside them (Fig.32). The cortical sinuses were located in the diffuse lymphoid tissue between the lymph nodules (Figs.13 and 31). The medullary sinuses were interposed between medullary trabeculae and medullary cords and continued into the efferent lymphatic vessels. In the lobulated nodes, the thick trabeculae took the role of the capsule of the lobules. So the paratrabecular sinuses of the thick trabeculae were regarded as the subcapsular sinuses of the lobules. The lumina of the subcapsular and paratrabecular sinuses were traversed by a dense network of interconnected reticular and fine elastic fibres. In young animals, the reticular fibres were the only fibres that traversed these sinuses. They originated from the fibrous capsule and trabeculae, crossed these sinuses in an irregular and radial fashion. Just before joining the cortex, the fibres were divided into many branches and continued with the reticular fibres of the corona, cortical sinuses and circumscribed areas that were found in the vicinity (Fig.29). In old animals, elastic fibres had a similar origin and distribution to the reticular fibres. The subcapsular and paratrabecular sinuses contained macrophages and white and red blood cells (Figs.13, 28 and 31). The sinuses were sometimes connected with the terminal branches of the capsular and trabecular arteries that were lined by endothelium. The blood cells were plenty in the primary mixed lymph nodes and increased with advancing age. The cortical sinuses were lined by a continuous layer of flat endothelial cells with basal lamina and supported by dense reticular and fine elastic fibres. The sinuses surrounded the lymph nodules and circumscribed areas and were separated from them by some cords of the diffuse lymphoid tissue. Wide cortical sinuses were observed in the lymph nodes whose nodules were not well developed such as in old animals. In young animals, the cortical sinuses in the primary mixed lymph nodes were difficult to see in the dense diffuse lymphoid tissue but were clearly observed in the light diffuse lymphoid tissue. With advancing age, they became evident and

92 were filled with blood. They contained a few lymphocytes, macrophages and erythrocytes. The medullary sinuses were also lined by a continuous layer of flat endothelial cells with a basal lamina and supported by dense reticular and fine elastic fibres. The sinuses formed a network of branching and anastomosing channels between the medullary cords. They joined the efferent lymphatic vessels at the hilus. They were more pronounced in the seconary mixed lymph nodes than in the primary mixed lymph nodes.

III.2.I.4.C. The Efferent Lymphatic Vessels The efferent lymphatic vessels were fewer in number but wider than the afferent ones. They left the lobes and nodes at their hiluses. They were provided with valves, which pointed away from the hilus. The walls of the efferent lymphatic vessels and their valves were similar in structure to that of the afferent lymphatic vessels but they had a thicker wall. These lymphatic vessels contained lymphocytes, and blood cells especially in the primary mixed lymph nodes.

III.2.I.5. The Circumscribed Areas In the diffuse lymphoid tissue, there were large cavities of different shapes, circumscribed areas, surrounded by sinuses, capillaries, sinusoids or cords of lymphoid tissue. The distribution of the circumscribed areas in the node was not constant in all lobes and even in the lobules of the same lobe. They were found more in the periphery of the lobules than in the central areas. They were connected with the subcapsular and paratrabecular sinuses and with terminal branches of the afferent lymphatic vessels (Figs.32, 34 and 35).

They were either filled with blood or contained lymphocytes and macrophages. The number and type of cells that were found within these circumscribed areas varied quite considerably according to the age. In young

93 animals, they were filled with lymphocytes. With advancing age, the erythrocytes increased in number substantially (Figs.34 and 35).

The circumscribed areas were surrounded by cells with pale and oval nuclei, like the endothelium of the lymphatic vessels, and were supported by reticular and fine elastic fibres (Fig.36). These fibres sent many fine branches to the lumen of these spaces. These circumscribed areas were fewer in the primary mixed lymph nodes than in the secondary ones.

III.2.I.6. The Vascularization The arteries entered the node through the hilus at one point, if the node was not lobulated, or at many point, if the node was lobulated. They ramified in the inter-lobar and inter-lobular connective tissue before penetrating the lobules through the hilus or capsule with the afferent lymphatic vessels. The large arterial branches initially ran within the thick trabeculae to the capsule and branched within it. These vessels entered the node by crossing the subcapsular sinuses. Arteries of different sizes were seen in the trabeculae and were characterized by having endothelial cells bulging into the lumen.

The arteries that entered through the hilus were larger than those, which entered through the capsule. The arteries that entered through the hilus reached the medulla and formed thin walled arterioles and capillaries between the medullary cords. Some branches continued to the cortex where they supplied the capillary plexuses of the diffuse lymphoid tissue and those of the lymph nodules. Many arterioles from different directions were directed to the nodules and branched into small capillaries before penetrating the nodules. Inside the nodules, these vessels further branched and were supported by reticular and fine elastic fibres. Special post-capillary venules with low cuboidal epithelium, usually termed high endothelial venules, originated from the cortical capillary plexuses and coarsed through the deep cortex to the medulla. In the medulla, they were continued with small venules lined by normal squamous endothelium. In the corticomedullary junction, the 94 arterioles had a thick wall and were lined by cuboidal endothelial cells bulging into the lumen. Inside the diffuse lymphatic tissue, venous sinuses of wide caliber with both low and high endothelial lining venules were present.

Some normal erythrocytes were found in the afferent lymphatics and a few in efferent lymphatics. The subcapsular and trabecular sinuses and circumscribed areas contained numerous apparently normal erythrocytes (Figs.34 and 37) whereas the cortical and medullary sinuses contained a few erythrocytes. A large number of apparently normal erythrocytes and erythrocytes of irregular shape were found in the interstitial spaces (Figs.31 and 37).

95

III.2.II. The Haemal Nodes

The haemal nodes were surrounded by capsule of dense irregular connective tissue, consisting mainly of collagen fibres (Fig.38) and a few elastic and reticular fibres. The collagen fibres were arranged in the form of small bundles. The elastic fibres were mainly found in the inner part of the capsule. Also elastic fibres were present in large blood and lymphatic vessels. Reticular fibres were scattered within the capsule. Smooth muscle fibres were absent in the capsule except in the tunica media of blood vessels. Larger blood vessels were situated tangential to the capsule. The outer surface of the capsule was merged with adjacent adipose tissue whereas the subcapsular sinus, which was lined by a continuous layer of endothelial cells, delineated the inner surface of the capsule.

The trabeculae were thin and originated from the inner surface of the capsule. They had the same structure as the capsule but were completely covered by endothelial cells of the paratrabecular sinuses and the elastic fibres were concentrated at the layers adjacent to the paratrabecular sinuses. Arterioles and lymphatic vessels were found within these trabeculae.

A number of afferent lymphatic vessels, which were characterized by thin walls and wide lumens, contained blood and pierced the capsule and opened directly into the subcapsular and paratrabecular sinuses and circumscribed areas. A single efferent lymphatic vessel was found at the hilus.

The stroma of the diffuse lymphoid tissue was supported by connective tissue framework consisting mainly of a network of reticular and fine elastic fibres. There was no clear demarcation between the cortex and medulla. The cortex was composed of a small number of primary lymph nodules and diffuse lymphatic tissue. The secondary lymph nodules were absent. The diffuse lymphatic tissue

96 contained small to medium size lymphocytes, plasma cells and a large number of erythrocytes (Figs.38 and 39). The erythrocytes were either attached to, or engulfed by, the macrophages.

Narrow medullary cords were found between the circumscribed areas and the medullary sinuses. They contained lymphocytes, reticular cells, erythrocytes, plasma cells and granulocytes (Fig.39).

The cortical and medullary sinuses were surrounded by continuous endothelial cells of dark flattened nuclei. They surrounded the circumscribed areas. The lumen of the sinuses was usually empty but in a few cases contained a few erythrocytes, macrophages and occasionally lymphocytes. The cortical sinuses were wider than the medullary ones. The medullary sinuses were connected to the efferent lymphatic vessels, which contained erythrocytes.

A large number of circumscribed areas were scattered all over the haemal node especially near the capsule and trabeculae and plenty in the medulla. Like the subcapsular and paratrabecular sinuses, the circumscribed areas were filled with blood. These areas were surrounded by discontinuous endothelial cells of pale and elongated or oval nuclei (Figs.38 and 39).

97

III.3. Electron Microscopy

The subcapsular and paratrabecular sinuses of lymph nodes were lined with a continuous layer of endothelial cells and a basal lamina on the trabecular and capsular sides (Fig.40). On the parenchymal side, the lining endothelium of the sinuses was discontinuous and the basal lamina was discontinuous or altogether absent. Adjacent endothelial cells on the continuous side (trabecular and capsular sides) of the sinus wall were joined together by tight junctions. The junctions were lacking on the inner side of the sinus adjacent to the parenchyma and, instead, large gaps were found between the endothelial cells, which had no long cytoplasmic projuctions like those of the continuous side of the sinus wall. These sinuses contained mainly erythrocytes, lymphocytes and macrophages (Fig.40). The sinuses communicated with each other through apertures found between adjacent sinus lining cells and gaps in the basal lamina. Erythrocytes were found passing through these apertures. Blood vessels including arterioles, capillaries and high postcapillary venules were seen in both the cortex and medulla. All three types of blood vessels showed a continuous nonfenestrated endothelium and pericytes were seen. Fibroblasts with elongated nuclei containing dense heterochromatin were seen around the capillaries. Nodular blood capillaries were not fenestrated and were surrounded by thick basal lamina. Lymphocytes were seen between the endothelium of the postcapillary venules. The erythrocytes reached the lymphatic sinuses of lymph nodes by way of the afferent lymphatics or by some of the terminal blood vessels within the capsule or trabeculae. Although erythrocytes were found in perivascular areas, yet no erythrocytes were seen crossing the wall of the capillaries or of the endothelial cells postcapillary venules. The cellular elements of the cortex were either loosely arranged or closely packed. The loose zones were composed of a large number of lymphocytes.

98 Interspersed between the lymphocytes were reticular cells, occasional macrophages and plasma cells .The intercellular spaces often contained reticular fibres. Areas of closely packed cells contained lymphocytes, reticular cells and macrophages. Lymphocytes by far outnumbered the other two types of cell. The cells of the lymph nodules were supported by a network of a large number of reticular cells and fibres and fine elastic fibres.

The lymphocytes showed a wide variation in the size and shape of their nuclei. They were subdivided into small, midium-sized and large lymphocytes. Dividing lymphocytes were seen in the germinal centre of some lymph nodules (Fig.41). The surface of the small lymphocyte was provided with a small number of short microvill, and the cell was mostly spherical in shape. The cytoplasm was in the form of a narrow rim surrounding the nucleus. The nucleus was either perfectly round, indented or oval in shape. The nucleus was characterized by a preponderance of heterochromatin that formed clumps at the periphery. A prominent nucleolus was almost always present. The scanty cytoplasm was poor in organelles. Centrioles and a small number of lysosomes were seen in a few lymphocytes. A few mitochondria and long profiles of rough endoplasmic reticulum were found in the cytoplasm (Fig.42). The medium-sized lymphocyte was round or oval and possessed short microvilli on their surface. The nucleus might be round, kidney-shaped or irregular in outline and the heterochromatin was mostly attached to the nuclear membrane. A prominent nucleolus was present. The cytoplasm contained a small number of organells that included mitochondria and, infrequently, Golgi apparatus. Free ribosomes and long cisternae of rough endoplasmic reticulum were more than in small lymphocytes (Fig.43). The large lymphocytes were relatively large and round, oval or irregular in shape, and the cytoplasm was abundant and lightly stained. The cell surface was slightly irregular and provided with short microvilli. The nucleus, with a few scattered heterochromatin, was mostly round or oval, but it might be irregular in

99 shape, and a nucleolus was seen in most of them. Long cisternae of rough endoplasmic reticulum, mitochondria and frequently Golgi apparatus were found.

Monocytes were mostly round in shape and the cell surface was provided with a few short microvilli and pseudopodia. The nucleus was kidney-shaped, and the heterochromatin was mostly attached to the nuclear membrane. The cytoplasm was relatively abundant, and the Golgi apparatus, mitochondria and many vacuoles were seen.

The red blood cells of the camel were elliptical in shape and nonnucleated. The cells were wide at their equator and had blunt tapering ends. The cytoplasm was highly basophilic and homogenous (Fig.40).

Neutrophils were plenty and their surfaces showed a few number of short microvilli. The cytoplasmic membrane-bound granules were plenty and of variable size. The nucleus was multilobulated and had up to five lobes, and the chromatin was mainly heterochromatin attached to the nuclear membrane, and a central euchromatin. Occasional mitochondria and Golgi apparatus were the only evident organelles present.

Eosinophils were also plenty and were characterized by having either bilobed or kidney-shaped or multilobulated nuclei. The cytoplasm was packed with large, ovoid and specific granules, which were membrane-bound, and their matrix contained bars of crystalloids. The cytoplasm contained a few amount of rough endoplasmic reticulum and scattered mitochondria (Fig.44).

Macrophages were seen inside the sinuses, in the diffuse lymphoid tissue, and inside germinal centres of the nodules. Macrophages possessed an irregular nucleus, which was small relative to the size of the cell. The chromatin was dispersed but a few heterochromatin was present at the periphery. A nucleolus was occasionally seen. The cell surface displayed pseudopodia especially in macrophages

100 situated inside the sinuses. The cytoplasm contained many vacuoles, mitochondria and several engulfed erythrocytes showing different stages of degradation. A few residual bodies were also found. Many lysosomes were seen in macrophages found inside the parenchyma of the node. The number of the lysosomes diminished and the number of vacuoles increased in macrophages laden with ingested material, especially erythrocytes. Several erythrocytes were engulfed by one macrophage. The common changes seen in the engulfed erythrocytes were: irregularity in their shape, granular apparance, especially at the periphery and then erythrocytes became tunnelized and fragmented by the cytoplasmic processes of the macrophages. In most cases, the macrophages were clearly outnumbered by the erythrocytes. Clusters of macrophages were common but their distribuation was not even in the node.

Plasma cells were plenty and were mainly found in the parenchyma of the node and in germinal centres of the lymph nodules. A few plasma cells were found inside the capsule and trabeculae. They were seen either singly or in groups. Plasma cells showed considerable variation in size and shape of the nucleus and the cell, and in the amount of the rough endoplasmic reticulum. The nucleus was spherical, oval or irregular in shape, but it showed its characteristic eccentric position. The clumps of heterochromatin were mostly peripheral and a prominent nucleolus was present. The cytoplasm was characterized by concentric cisternae of rough endoplasmic reticulum, which were long and occupied almost the whole cytoplasm, and some of them were distended and filled with flocculent dense material. Some spherical and dense bodies were observed outside the cisternae of rough endoplasmic reticulum. The Golgi apparatus was well developed and consisted of many stacks of cisternae and vacuoles (Fig.45).

Reticular cells were characterized by having elongated, oval or irregular nuclei with many indentations and a few heterochromatin which was found mainly at the periphery. The cytoplasm was fairly rich in organelles including free ribosomes, mitochondria, rough endoplasmic reticulum and Golgi apparatus. Some

101 of the reticular cells showed very long and tapering cytoplasmic processes. Reticular fibres were often associated with processes of reticular cells. Reticular cells extended long cytoplasmic processes around erythrocytes.

102

III.4.Morphometry

The morphometric analysis was carried out in six mammary lymph nodes (three right and three left). The analysis revealed that the connective tissue of the capsule and the trabeculae, constituted 16.86% (8.33 cm³±0.68) of the volume of the right lymph node and 18.18% (8.94 cm³±2.72) of the volume of the left lymph node, the right germinal centres 4.32% (2.34 cm³±1.35) and the left ones 3.65% (1.94 cm³±1.08), the right corona 5.84% (3.08 cm³±1.18) and the left one 4.92% (2.58 cm³±1.18), the right diffuse lymphatic tissues 45.3% (23.53 cm³±6.61) and the left ones 44.62% (23.5 cm³±9.81), the right blood and lymph vessels 17.88% (9.12 cm³±2.07) and the left one 19.02% (9.42 cm³±2.1), the right sinuses 9.07% (4.56 cm³±0.28) and the left ones 9.03% (4.62 cm³±1.7) and the right circumscribed areas 0.73% (0.37 cm³±0.085) and the left ones 0.58% (0.33 cm³±0.25).

The mean absolute volume of the fresh right lymph node was about 51.33 cm³±10.26, while that of the left lymph node was 51.33 cm³±17.

Tables 5-15 show the result of the morphometric analysis of the right and left mammary lymph nodes of the dromedary.

103 Table 5: Animal number 1. This table shows data obtained by point counting of fields of a sample section of the left mammary lymph node. F.No. C.T. G. C. C. D.L. B.&L. S. C.A. T.N. T. V. P. 1 11 16 12 41 16 4 ---- 100 2 3 2 4 58 30 3 ---- 100 3 4 5 7 55 16 11 2 100 4 20 2 7 54 12 5 ---- 100 5 26 2 10 42 18 2 ---- 100 6 4 2 5 55 25 5 4 100 7 7 ------78 11 4 ---- 100 8 12 ------63 12 13 ---- 100 9 22 ------61 10 7 ---- 100 10 8 4 3 69 14 2 ---- 100 11 3 2 3 74 13 2 3 100 12 38 7 10 28 9 8 ---- 100 13 13 ------62 18 7 ---- 100 14 8 13 9 45 16 6 3 100 15 9 8 6 64 12 1 ---- 100 16 13 ------68 10 9 ---- 100 17 6 ------76 8 10 ---- 100 18 23 ------58 8 11 ---- 100 19 32 ------45 8 15 ---- 100 20 1 1 2 71 15 8 2 100 21 5 1 4 76 6 8 ---- 100 22 4 1 2 71 17 2 3 100 23 25 4 6 49 9 7 ---- 100 24 25 14 13 25 6 17 ---- 100 25 43 ---- 4 31 6 12 4 100 26 11 ---- 4 71 6 8 ---- 100 27 1 1 3 75 17 3 ---- 100 28 60 ------26 6 8 ---- 100 29 51 ------34 7 6 2 100 30 54 ------16 11 19 ---- 100

C. = Corona. S. = Sinuses. C.T. = Connective Tissue. F.No. = Field Number. C.A. = Circumscribed Areas. G.C. = Germinal Centre. D.L.T. = Diffuse Lymphatic Tissue. B.&L.V. = Blood and Lymph Vessels. T.N.P. = Total Number of Points.

104 Table 6: Animal number 1. The total points counted, the volume fraction and the absolute volume of each component of the right mammary lymph node. Absolute volume of the right mammary lymph node was 54 cm³. Section C.T. G.C C. D.L.T. B.&L. S. C.A. Total No. V. 1 605 382 417 2597 578 464 57 5100 2 919 187 293 2562 725 409 5 5100 3 993 187 308 2180 614 416 2 4700 4 825 229 297 2784 836 505 24 5500 5 659 121 199 2298 948 333 42 4600 T.C. 4001 1106 1514 12421 3701 2127 130 25000 Vv.% 16.00 4.40 6.06 49.68 14.8 8.519 0.52 100 Abs.V.cm³ 8.64 2.39 3.27 26.83 7.99 4.60 0.28 54

Table 7: Animal number 1. The total points counted, the volume fraction and the absolute volume of each component of the left mammary lymph node. Absolute volume of the left mammary lymph node was 64 cm³. Section C.T. G.C C. D.L.T. B.&L. S. C.A. Total No. V. 1 542 85 114 1641 372 223 23 3000 2 365 83 149 1978 534 367 24 3500 3 699 122 196 2526 743 443 71 4800 4 1155 221 297 2024 775 681 47 5200 5 1395 140 209 2208 1017 491 40 5500 T.C. 4156 651 965 10377 3441 2205 205 22000 Vv.% 18.89 2.96 4.39 47.17 15.64 10.02 0.93 100 Abs.V.cm³ 12.09 1.89 2.81 30.19 10.01 6.41 0.60 64

C. = Corona. S. = Sinuses. C.T. = Connective Tissue. Vv. = Volume Fraction. C.A. = Circumscribed Areas. G.C. = Germinal Centre. D.L.T. = Diffuse Lymphatic Tissue. B.&L.V. = Blood and Lymph Vessels. Abs.V. = Absolute Volume. T.C.=Total Count.

105 Table 8: Animal number 2. The total points counted, the volume fraction and the absolute volume of each component of the right lymph node. Absolute volume of the right lymph node was 40 cm³. Section C.T. G.C C. D.L.T. B.&L. S. C.A. Total No. V. 1 1696 206 347 1708 1101 760 82 5900 2 1182 120 233 2792 1015 599 22 6000 3 1489 87 192 2468 1201 540 23 5600 4 1176 161 287 2030 1096 591 59 5400 5 659 66 140 1513 743 326 53 3500 T.C. 5802 640 1199 10511 5193 2816 239 26400 Vv.% 21.98 2.42 4.54 39.81 19.67 10.67 0.91 100 Abs.V.cm³ 8.79 0.97 1.82 15.92 7.87 4.27 0.36 40

Table 9: Animal number 2. The total points counted, the volume fraction and the absolute volume of each component of the left lymph node. Absolute volume of the left lymph node was 32 cm³. Section C.T. G.C C. D.L.T. B.&L. S. C.A. Total No. V. 1 1149 210 294 2225 1119 483 20 5500 2 1343 117 238 1899 1284 514 5 5400 3 1213 283 339 2708 1464 565 28 6600 4 1397 95 182 2341 1225 732 28 6000 5 1577 99 140 2003 1378 477 26 5700 T.C. 6679 804 1193 11176 6470 2771 107 29200 Vv.% 22.87 2.75 4.09 38.27 22.16 9.49 0.37 100 Abs.V.cm³ 7.32 0.88 1.31 12.24 7.09 3.04 0.12 32

C. = Corona. S. = Sinuses. C.T. = Connective Tissue. Vv. = Volume Fraction. C.A. = Circumscribed Areas. G.C. = Germinal Centre. D.L.T. = Diffused Lymphatic Tissue. B.&L.V. = Blood and Lymph Vessels. Abs.V. = Absolute Volume. T.C.=Total Count.

106 Table 10: Animal number 3. The total points counted, the volume fraction and the absolute volume of each component of the right lymph node. Absolute volume of the right lymph node was 60 cm³. Section C.T. G.C C. D.L.T. B.&L. S. C.A. Total No. V. 1 631 527 568 1933 993 507 41 5200 2 935 201 300 2751 1083 652 78 6000 3 668 207 259 2661 1062 307 36 5200 4 677 346 400 3144 1259 440 34 6300 5 589 421 393 24416 935 326 20 5100 T.C. 3500 1702 1920 12905 5332 2232 209 27800 Vv. 12.59 6.12 6.91 46.42 19.18 8.03 0.75 100 Abs.V.cm³ 7.55 3.67 4.15 27.85 11.51 4.82 0.45 60

Table 11: Animal number 3. The total points counted, the volume fraction and the absolute volume of each component of the left lymph node. Absolute volume of the left lymph node was 58 cm³. Section C.T. G.C C. D.L.T. B.&L. S. C.A. Total No. V. 1 587 282 370 2678 1192 467 24 2600 2 599 252 384 2802 959 480 24 5500 3 666 340 347 3132 1118 369 28 6000 4 778 206 242 2470 865 421 18 5000 5 925 378 396 2380 1219 374 28 5700 T.C. 3555 1458 1739 13462 5353 2111 122 27800 Vv. 12.79 5.24 60.26 48.42 19.26 7.59 0.44 100 Abs.V.cm³ 7.42 3.04 3.63 28.08 11.17 4.40 0.26 58

C. = Corona. S. = Sinuses. C.T. = Connective Tissue. Vv. = Volume Fraction. C.A. = Circumscribed Areas. G.C. = Germinal Centre. D.L.T. = Diffused Lymphatic Tissue. B.&L.V. = Blood and Lymph Vessels. Abs.V. = Absolute Volume. T.C.=Total Count.

107 Table 12: The absolute volumes of the different components of the right lymph node, the absolute volume of the whole right lymph node and the standard deviation of these parameters. Animal C.T. G.C. C. D.L.T. B.&L.V. S. C.A. Total Number Abs.V. Abs.V. Abs.V. Abs.V. Abs.V. Abs.V. Abs.V. Abs.V. cm³ cm³ cm³ cm³ cm³ cm³ cm³ cm³ 1 8.64 2.39 3.27 26.83 7.99 4.60 0.28 54

2 8.79 0.97 1.82 15.92 7.87 4.27 0.36 40 3 7.55 3.67 4.15 27.85 11.51 4.82 0.45 60 Total 24.98 7.03 9.24 70.60 27.37 13.69 1.09 154 Mean 8.33 2.34 3.08 23.53 9.12 4.56 0.36 51.33

S.D. 0.68 1.35 1.18 6.61 2.07 0.28 0.08 10.26

Table 13: The absolute volumes of the different components of the left lymph node, the absolute volume of the whole left lymph node and the standard deviation of these parameters. Animal C.T. G.C. C. D.L.T. B.&L.V. S. C.A. Total Number Abs.V. Abs.V. Abs.V. Abs.V. Abs.V. Abs.V. Abs.V. Abs.V cm³ cm³ cm³ cm³ cm³ cm³ cm³ cm³ 1 12.09 1.89 2.81 30.19 10.01 6.41 0.60 64 2 7.32 0.88 1.31 12.24 7.09 3.04 0.12 32 3 7.42 3.04 3.63 28.08 11.17 4.40 0.26 58 Total 26.8 5.81 7.75 70.51 28.27 13.85 0.98 154 Mean 8.94 1.94 2.58 23.50 9.42 4.62 0.33 51.33

S.D. 2.72 1.08 1.18 9.81 2.10 1.70 0.25 17.00

C. = Corona. S. = Sinuses. C.T. = Connective Tissue. Vv. = Volume Fraction. C.A. = Circumscribed Areas. G.C. = Germinal Centre. D.L.T. = Diffused Lymphatic Tissue. B.&L.V. = Blood and Lymph Vessels. Abs.V. =Absolute Volume. S.D. = Standard Deviation.

108 Table 14: The volume fraction (Vv.) and the standard deviation (S.D.) of each component of the three right lymph nodes used in this study in addition to their mean values. Animal C.T. G.C. C. D.L.T. B.&L. S. (Vv.) C.A. Total Number (Vv.) (Vv.) (Vv.) (Vv.) V.(Vv.) % (Vv.) (Vv.) % % % % % % % 1 16 4.43 6.06 49.86 14.8 8.51 0.52 100 2 21.98 2.42 4.54 39.81 19.67 10.67 0.91 100 3 12.59 6.12 6.91 46.42 19.18 8.03 0.75 100 Total 50.57 12.97 17.51 135.91 53.65 27.21 2.18 300 Mean 16.86 4.32 5.84 45.3 17.88 9.07 0.73 100

S.D. 4.75 1.85 1.20 5.03 2.68 1.41 0.20 0

Table 15: The volume fraction (Vv.) and the standard deviation (S.D.) of each component of the three left lymph nodes used in this study in addition to their mean values. Animal C.T. G.C. C. (Vv.) D.L.T. B.&L. S. (Vv.) C.A. Total Number (Vv.) (Vv.) (Vv.) V.(Vv.) (Vv.) (Vv.) 1 18.89 2.96 4.39 47.17 15.64 10.02 0.93 100 2 22.87 2.75 4.09 38.27 22.16 9.49 0.37 100 3 12.79 5.24 6.26 48.42 19.26 7.59 0.44 100 Total 54.55 10.95 14.74 133.86 57.06 27.10 1.74 300 Mean 18.18 3.65 4.92 44.62 19.02 9.03 0.58 100

S.D. 5.08 1.38 1.10 5.54 3.27 1.28 0.31 0

C. = Corona. S. = Sinuses. C.T. = Connective Tissue. Vv. = Volume Fraction. C.A. = Circumscribed Areas. G.C. = Germinal Centre. D.L.T. = Diffused Lymphatic Tissue. B.&L.V. = Blood and Lymph Vessels. S.D. = Standard Deviation. T.V. = Total Volume.

109

Fig.III.1 The volume fraction of components of the right and left mammary lymph nodes

50 45 40 35 30 Right 25 Left 20 15

Percentage of components 10 5 0 1234567 The volume fraction of components

1= Connective Tissue. 2= Germinal Centre. 3= Corona. 4= Diffused Lymphatic Tissue. 5= Blood and Lymph Vessels. 6= Sinuses. 7= Circumscribed Areas.

110

CHAPTER FOUR DISCUSSION

111

CHAPTER FOUR DISCUSSION IV.1.Gross Anatomy

The qualitative and quantitive distribution of some of the superficial and deep lymph nodes of the camel suggest that the overall topography of the lymph nodes of the camel resembles that of the ruminants as described by May (1970), Dyce and Wensing (1971), and Sisson and Grossman (1975), but differences occur in the location and in the number of the nodes in the different lymphocentres. Other notable features are the absence of some lymph nodes like the prefemoral and atrial lymph nodes, which are present in most domestic mammals, and most of the superficial lymph nodes are readily accessible for palpation in the camel.

IV.1.1.The Lymph Nodes of the Head The present findings on the lymph nodes of the head agree with those reported by Taher (1962), Smuts and Bezuidenhout (1987) and Abdel-Magied et al. (2001) in the camel with a few modifications in the nomenclature of some of the lymph nodes. The lymp nodes of the head region of the camel are grouped, as in other domestic animals, into three lymphocentres.

112 In the present investigation, the parotid lymphocentre consists of the parotid lymph nodes. A similar finding has already been reported in the camel (Taher, 1962; Smuts and Bezuidenhout, 1987; Osman, 1988; Abdel-Magied et al., 2001), buffalo (El-Gendi, 1971), ox (Sisson and Grossman, 1975; Constantinescu et al., 1988), sheep and goat (May, 1970; Dyce et al., 1987), dog (Miller et al., 1964; Chretien et al., 1967) and cat (Sisson and Grossman, 1975) . The present results agree with those of Taher (1962) in the camel, Miller et al. (1964), Chretien et al. (1967) in the dog and Sisson and Grossman (1975) in the cat, that the accessory parotid lymph nodes are absent. However, the presence of relatively small nodes could be considered as a prominent feature of this centre in the buffalo (El-Gendi, 1971), ox (Sisson and Grossman, 1975; Constantinescu et al., 1988) and sheep (May, 1970).

The mandibular lymphocentre of the camel comprises the mandibular and pterygoid nodes. The present findings on the mandibular nodes agree with those given by Taher (1962) and Smuts and Bezuidenhout (1987) in the camel, as well as, in the buffalo (El-Gendi, 1971) and ox (Sisson and Grossman, 1975). The mandibular lymph node of the camel is larger than the parotid and retropharyngeal lymph nodes. This finding is not in agreement with Abdel- Magied et al. (2001), who reported that the retropharyngeal node is the largest. The accessory mandibular nodes in the camel are absent. However, the presence of accessory small nodes could be considered as a permanent feature in the buffalo, dog, pig and cat (Chretien et al., 1967; El-Gendi, 1971; Sisson and Grossman, 1975; Dyce et al., 1987).

113 El-Gendi (1971) states that, the pterygoid node is present in three out of thirty of the specimens, whereas in the present investigation; this node is found in 20% of the cases. In the ox, this node is found in the majority of the cases (Sisson and Grossman, 1975). On the Other hand, this node is absent in the dog (Miller et al., 1964), horse and pig (Sisson and Grossman, 1975).

In the present investigation, the retropharyngeal lymphocentre consists only of the medial retropharyngeal nodes. A similar finding has already been described in the camel by Smuts and Bezuidenhout (1987). A modifcation in the nomenclature of these nodes in the camel is reported by Taher (1962) who named them parapharyngeal nodes whereas Abdel-Magid (1986) and Abdel- Magied et al. (2001) called them the lateral retropharyngeal nodes. In other domestic mammals, this centre comprises the medial and lateral retropharyngeal nodes (Sisson and Grossman, 1975; Dyce et al., 1987).

IV.1.2.The Cervical Lymph Nodes The superficial cervical lymphocentre of domestic mammals is grouped into superficial cervical (prescapular) and accessory superficial cervical lymph nodes that show some variation. It is grouped into medial and lateral superficial cervical lymph nodes in the dog (Chretien et al., 1967), cranial, middle and caudal superficial cervical lymph nodes in sheep (May, 1970) and dorsal, middle and ventral superficial cervical lymph nodes in the pig (Sisson and Grossman, 1975; Dyce et al., 1987). The classifcation of this centre into superficial dorsal and ventral cervical lymph nodes is reported by Sugimura (1962) in cats and Miller et al. (1964) in dogs. This latter classification is found to be more suitable to the camel. The presence of the haemal nodes alongside the lymph

114 node is considered to be a prominent feature in ruminants (May, 1970; El- Gendi, 1971; Tanudimadja and Ghoshal, 1973b; Sisson and Grossman, 1975).

The deep cervical lymphocentre of the camel is nearly similar to the corresponding centre in other domestic mammals in which cranial, middle and caudal groups are demonstrated except in sheep (Sisson and Grossman, 1975) and cats (Sugimura, Kudo and Takahata, 1955) where the cranial and middle groups are absent and in the dog (Sisson and Grossman, 1975) where the middle and caudal groups are lacking. In the ox and horse, the components of the deep cervical lymphocentre are frequently confluent (Sisson and Grossman, 1975) but in the present study, they are always well demarcated from each other and a clear asymmetry in their position, size and number is noted. IV.1.3.Some Lymphocentres and Lymph Nodes of The Thorax According to the present study, it is evident that the intercostal nodes are similar to those described in the camel by Taher (1962) and Smuts and Bezuidenhout (1987). But these nodes differ from those described in other domestic mammals by Sisson and Grossman (1975), El-Gendi (1971) and Chretien et al., (1967) in that their locations are not similar.

The mediastinal lymphocentre of the camel consists of cranial, middle and caudal mediastinal lymph nodes. This classification agrees with the description of Smuts and Bezuidenhout (1987) but is different from that of Taher (1962) who named the middle mediastinal lymph nodes as dorsal mediastinal nodes. The sternal and paratracheal, dorsal mediastinal, ventral mediastinal and nuchal nodes are included in this centre in the cat (Sugimura, 1962), sheep (May, 1970), ox (Dyce and Wensing, 1971) and horse (Sisson and

115 Grossman, 1975). Also in ruminants, the presence of a large number of haemal nodes alongside the lymph node is a remarkable feature (May, 1970; El-Gendi, 1971; Sisson and Grossman, 1975; Dyce et al., 1987).

It must be noted that the cranial mediastinal nodes predominate in the camel (Taher, 1962; Smuts and Bezuidenhout, 1987) and other domestic mammals (May, 1970; El-Gendi, 1971; Sisson and Grossman, 1975), whereas the middle mediastinal nodes are absent in sheep, pig, dog and cat (Sisson and Grossman, 1975). In the camel, Taher (1962) reported the presence of the right and left tracheobronchial nodes, whereas Smuts and Bezuidenhout (1987) reported the absence of the right tracheobronchial node and the presence of the left and middle ones.

In the ruminants, Dyce and Wensing (1971) and Dyce et al. (1987) agree that, the tracheobroncheal nodes are sometimes regarded as forming a separate lymphocentre and sometimes are assigned to the mediastinal lymphocentre. In the cat, Sugimura (1962) reported the presence of the cranial tracheobroncheal nodes, while Sisson and Grossman (1975) deny their presence. Bradley (1946) gave another classification in the horse in which the bronchial lymph nodes are grouped into dorsal and ventral nodes. It is pertinent to note that the cranial and caudal tracheobronchial, pulmonary, right and left pericardial and diphragmatic lymph nodes of domestic mammals (Bradley, 1946; Miller et al., 1962; Sugimura, 1962; El- Gendi, 1971; Sisson and Grossman, 1975) are absent in the camel.

116 IV.1.4. Some Lymphocentres and Nodes of the Abdominal and Pelvic Wall, Viscera and Hindlimb In the camel, the lumbar lymphocentre includes the lumbar aortic and renal lymph nodes (Smuts and Bezuidenhout, 1987). In the buffalo and ox (El- Gendi, 1971; Sisson and Grossman, 1975), additional nodes, known as the proper lumbar lymph nodes, are found. Sisson and Grossman (1975) include the ovarian nodes to this centre in the horse. In the cat the lumbar group includes the cranial and caudal lumbar lymph nodes (Sugimura, 1962). The lumbar aortic lymph nodes are not clearly distinguishable from the medial iliac nodes in all domestic mammals, the cranial and caudal mesenteric and renal nodes in the ox and horse, the the accessory hepatic and celiac nodes in the ox and from the uterine and ovarian nodes in the horse (Sisson and Grossman, 1975). In the camel, the lumbar aortic nodes are always well demarcated from adjacent nodes.

The present study on the renal lymph nodes supports the findings of Smuts and Bezuidenhout (1987) in that these nodes are found along the blood vessels. The renal nodes are embedded in adipose tissue and because of their small size they may escape notice. This is also true for the lumbar aortic nodes of the dog (Miller et al., 1964; Sisson and Grossman, 1975).

The superficial inguinal lymphocentre of the camel constitutes the scrotal nodes in male and mammary nodes in female. The present findings are similar to those of Smuts and Bezuidenhout (1987) in the camel, and Sisson and Grossman (1975) and Dyce et al. (1987) in other mammals. However, Taher (1962) and Miller et al. (1964) include this node to the nodes of the

117 pelvic limb in the camel and the dog respectively. The accessory superficial inguinal lymph nodes of the cat (Sugimura et al., 1956), buffalo (El-Gendi, 1971), horse (Sisson and Grossman, 1975) and pig (Dyce et al., 1987) are absent in the camel. It should be stated that in both male and female of the camel the superficial inguinal lymph node has a peculiar relationship with the external pudendal artery. This relationship may have some influence on the physiology of the organ supplied by that artery in case of enlargement of the node and this observation supports the findings of El-Gendi (1971) in the buffalo.

The subiliac lymph node, in most domestic animals, forms a single, large and elongated node, but in the horse and pig it forms a conglomerate of small nodes that reach 15-20 nodes in the horse (Sisson and Grossman, 1975), but in the camel these nodes are totally absent.

The present study supports the findings of Smuts and Bezuidenhout (1987) in the camel and Sisson and Grossman (1975) and Dyce et al. (1987) in ruminants that the tuberal lymph nodes are found near the sacrotuberal ligament and covered by the skin. The present study is in agreement with the findings of Smuts and Bezuidenhout (1987) that the gastric lymph nodes in the camel are divided into six groups according to their location to the different compartements of the stomach. Taher (1962) described similar groups of nodes in camel but with a few modifications in the nomenclature of some of the lymph nodes. The gastric nodes of ruminants are divided into eight groups (May, 1970; El-Gendi, 1971; Saleh and Ibrahim, 1975; Sisson and Grossman, 1975).

118

IV.2.Histology

The lymphoid nodes of mammals are found in three forms: lymph nodes, haemolymph (mixed) nodes and haemal nodes. The haemolymph nodes are confined to certain locations, usually in association with specific visceral organs (Banks, 1993).

IV.2.I.The Lymph and Haemolymph Nodes

The camel lymph nodes are affected by age and they are gradually transformed into haemolymph nodes and are present in locations that are typical of the homologues in other mammals. Thus, the camel lymph nodes under consideration are neither typical lymph nodes nor typical haemolymph

119 nodes. The presence of afferent lymphatics and circumscribed areas filled with blood in the camel lymph nodes suggest that they are functionally similar to the haemolymph nodes of other mammals, which have the ability to cope with both lymph-borne and blood-borne antigens (Abbas et al., 1994). Lymph nodes do not contain extravascular blood and blood-filled sinuses except in pathological conditions (Lucke, Davies, Wood and Whitbread, 1987; Welsh, Griffon and Whitbread, 1999). However, normal mammary lymph nodes of the cow may contain erythrocytes in their parenchyma (Hampl, 1978), and blood sinuses are normally present in the haemal and haemolymph nodes of some mammals (Gargiulo et al., 1987; Abu- Hijleh and Scotherne, 1996; Sakita et al., 1997). In the camel, erythrocytes were reported in lymph nodes of apparently healthy camels in this study and in the reports of Osman (1988), Sharfee (1989) and Abdel-Magied et al. (2001). Thus the presence of blood is an apparently normal feature of camel nodes. The name mixed lymph nodes was introduced by Osman (1988) in order to avoid confusion arising from using other existing terms such as haemolymph nodes or haemal lymph nodes. In this study, some of the mixed lymph nodes showed erythrocytes all over the node and at all ages, whereas others showed erythrocytes only in old animals. To avoid confusion between the two groups, the first group is termed as primary mixed lymph nodes (PMLN), while the other group is termed as secondary mixed lymph nodes (SMLN). This classification is adopted by Sharfee (1989). However, Abdel-Magid (1986) reports that there were no erythrocytes in the retropharyngeal lymph nodes of the camel. This may be due to the very small sections he took for the ultrastructure or the sections were taken from young animals. Different structural variations of the camel nodes are noted in the present study. Some variations seem to be related to the degree of

120 differentiation, the location of the nodes, or to age. Moreover, these three factors are also related to one another.

IV.2.I.1.The Capsule and Trabeculae The lymph node of the camel is covered by a capsule consisting mainly of large bundles of collagen fibres with a few elastic and reticular fibres. The PMLN possesses a well-developed capsule and trabeculae more than the SMLN. Thick fibrous trabeculae originate from the inner wall of the capsule and divide the node into many lobes. These results are in agreement with those of Osman (1988) and Sharfee (1989) in the same speices. The present study confirms the earliar reports of Furuta (1949) in hamster and rats, and Sugimura (1962) in cats that the thickness of the capsule is increases with advancing age. However, Hwang et al. (1968) and Dellmann and Brown (1981) state that, the capsule in the rat and human haemolymph nodes becomes thinner with advancing age. No smooth muscle fibres were found in the capsule of the lymph nodes and haemolymph nodes of the rat (Nopajaroonsri et al., 1971) and the mixed lymph nodes of the camel (Osman, 1988; Sharfee, 1989). This was confirmed in the present study. However, the capsule and trabeculae of the lymph nodes of the bovine (Folse et al., 1975), man and rat (Pastukhova, 1986), goat (Faroon et al., 1987) and camel (Abdel-Magied et al., 2001) contain smooth muscle fibres. Also smooth muscle fibres were reported in the capsule of the bovine haemolymph nodes (Folse et al., 1975). The large peripheral lymph nodes have prominent trabeculae but the nodes that are found deep in the body as in the abdominal cavity, have thin and often interrupted trabeculae (Fawcett, 1994). This was confirmed in the present study in PMLN and SMLN respectively.

121 Fine trabeculae were present inbetween the lymphatic sinuses of the rat (Nopajaroonsri et al., 1971) and camel (Osman, 1988; Sharfee, 1989). Similar findings were obtained in this investigation. In the present study, the hilar structure varied in the different groups of the lymph nodes. The simplest form of the hilus is seen in the SMLN and it is similar to a typical hilus that is found in lymph nodes of most domestic animals (Leeson and Leeson, 1970; Gartner and Hiatt, 1997). However, pig lymph nodes lack a typical hilus (Dellmann and Brown, 1981; Spalding and Heath, 1986) and possess two types of hilus, the afferent type hilus and the efferent type hilus (Hoshi et al., 1986). On the other hand, the large nodes of the PMLN in the camel have multiple hiluses.

IV.2.I.2.The Parenchyma The lymph nodes and haemolymph nodes of most mammals are divided into cortex and medulla (Sugimura, 1962; Junqueira et al., 1998; Young and Heath, 2000). Because of the regional difference in the arrangement of the cortex and medulla there is a dispute in rodent lymph nodes. Job (1915) classified the rat nodes into two types: in type I, the cortex covers the medulla and in type II, the cortex and medulla are situated at opposite sides of the nodes. Type II is found more conspicuously in the deep nodes than in the superficial ones. However, in man, Denz (1947) stated that the deep nodes have more developed cortex than those of the superficial ones. In wistar rat, the node is divided into cortex, paracortex and medulla (Nopajaroonsri et al., 1971). Concerning the histological architecture of pig lymph nodes, some authors are of the opinion that there is a reverse interrelation between the cortical areas and the medullary ones; the central region of the nodes is occupied by the cortical tissue, whereas the medullary tissue is situated in the

122 periphery of the nodes (Merighi et al., 1986; Spalding and Heath, 1986; Banks, 1993; Tizard, 2000). In the camel, the parenchyma consists of lymph nodules, anodular dense lymphoid tissue and diffuse lymphoid tissue (Abdel-Magied et al., 2001). None of these subdivitions could fit well in the present study. The present results agree with those of Osman (1988) that in the camel mixed lymph nodes, each lobule could be compared to the whole lymph node of other species in which there is an outer cortex and inner medulla. The present results also agree with those of Sharfee (1989) that the arrangement of the cortex and medulla is irregularly demarcated. In wistar rat lymph nodes, the nodules are situated mainly in the cortex and rarely in the paracortex (Nopajaroonsri et al., 1971), while in most domestic mammals, the nodules are situated in the outer cortex (Banks, 1993; Ross et al., 1995; Weir and Stewart, 1997). However, the present study confirms the report of Osman (1988) that, in camel mixed lymph nodes, the nodules are situated at the periphery of the lobules below the capsule and on either side of the trabeculae. The present study in the camel confirms the reports of Heath and Nikles (1991) that there is no constant relationship between the number of the nodules and location of the node in the horse. Banks (1993) noticed that fusion of cortical nodules is common. This is also true for the camel in the present observation. Sugimura (1962) and Osman (1988) reported the presence of arterioles and capillaries in the lymph nodules of the cat and the camel respectively. The present results confirm the presence of capillaries only. However, no blood vessels were seen in the follicles of the wistar rat (Nopajaroonsri et al., 1971). Previously, the lymph nodules were termed germinal centres and are divided into light and dark zones in rats (Kindred, 1938) and cats (Rohlich,

123 1933; Sugimura, 1962), and in human the nodules are divided into active centre and resting one (Denz, 1947). Recently, the term secondary nodule is adopted and is divided into a paler central zone called germinal centre and outer dark corona. The present study confirms the report of Fawcett (1994) that the corona is directed toward both the marginal sinuses and the paratrabecular sinuses. This may be due to trapping of the incoming lymphocytes with lymph. The pale staining of the germinal centres is due to the fact that the large lymphocytes andmacrophages have more cytoplasm than the small ones and their nuclei are more euchromatic (Leeson and Leeson, 1970; Fawcett, 1994) and due to the presence of a few cells in the germinal centres in comparison to the corona (Banks, 1993). The present study confirms these results. The germinal centres contain mainly large and small lymphocytes (Nopajaroonsri et al., 1971; Osman, 1988), or small and medium-sized lymphocytes (Abdel-Magied et al., 2001). The present study is in agreement with Sharfee (1989) in the camel that the main cell types of the germinal centre are the large and medium-sized lymphocytes. The present study is also in agreement with those of Osman (1988), Sharfee (1989) and Abdel-Magied et al. (2001) that some lymphocytes with mitotic figures, and plasma cells are observed. A few reticular fibres are present in the germinal centre of the camel mixed lymph nodes (Sharfee, 1989). This finding is in agreement with the present study. However, Osman (1988) and Abdel-Magied et al. (2001) stated that the lymph nodules were devoid of reticular fibres. It is probable that specimens were collected from young animals.

IV.2.I.3.The Lymph Circulation

124 The present study supports the findings of Nikles and Heath (1992), Burkitt et al. (1997) and Young and Heath (2000) that, in most mammals, the afferent lymphatic vessels approach the node and divide into several small branches that enter the node at multiple sites on its convex surface. However, the intranodal lymph flow in the pig lymph nodes is reversed as a result of the characteristic structure of the pig node; the afferent lymph vessels enter the node at the hilus and the efferent lymph vessels leave from the convex peripheral surface of the node (Hoshi et al., 1986). The present study also supports the findings of Osman (1988), Abdel- Magied et al. (2001), Fawcett (1994) and Junqueira et al. (1998) that the lymphatic vessels are equipped with valves. This is to ensure unidirectional flow of lymph through the node. In dogs, the valves are found adjacent to the point of entery of the vessels into the node (Belz and Heath, 1995a). The present observations agree with those of Dellmann and Brown (1981), Osman (1988), Sharfee (1989) and Spalding and Heath (1989b) that the subcapsular and paratrabecular sinuses are lined with a continuous layer of endothelial cells at the capsular and trabecular sides, but the endothelium is discontinuous toward the parenchyma of the node. These observations indicate that sinus walls adjacent to connective tissue serve as a barrier to cell movement, but those adjacent to the parenchyma possess gaps, with cells in apparent transit between sinus lumen and parenchyma. The presence of reticular and elastic fibres traversing the lumina of the sinuses in the nodes of the camel, and dog (Dellmann and Brown, 1981) and human (Roitt, 1997) is a necessary arrangement for slowing the rate of flow of lymph. This slowing of the rate of flow facilitates antigen-cell intraction, and phagocytic activity of macrophages.

125 The subcapsular and paratrabecular sinuses of the lymph node and haemolymph node of the wistar rat and mouse are relatively small in comparison with the medullary sinuses (Nopajaroonsri et al., 1971; Kowala and Schoefl, 1986). This is also true for the PMLN in the present study. The present investigation confirms the findings in the cat (Sugimura, 1962) that the subcapsular sinuses are narrow, but some times, wide sinuses are observed in the lymph nodes whose nodules are not well developed. The present results support the findings of Osman (1988) and Sharfee (1989) in the camel, and Nopajaroonsri et al. (1971) in the rat and mouse that both lymphocytes and erythrocytes were present inside the lumen of the sinuses of the lymph nodes. In camel mixed lymph node (Osman, 1988; Sharfee, 1989) and rat haemolymph node (Andreason and Gottlieb, 1946; Turner, 1969), the majortity of the red blood cells were found free in the sinusoids, but some of them were attached to the surface of macrophages. In the camel mixed lymph nodes, in this study, plenty of red blood cells were found in the cortical and medullary sinuses and some red blood cells were found attached to, or engulfed by, macrophages. The present study confirms the previous results of Sharfee (1989) that macrophages are found singly or in groups in the medullary cords and in the dense lymphoid tissue and some macrophages are ingesting red blood cells.

Plasma cells were reported inside the sinuses of lymph nodes and haemolymph nodes of rats (Nopajaroonsri et al., 1971, 1974). The present observations agree with Sharfee (1989) that in the camel mixed lymph nodes the plasma cells were present in the subcapsular and paratrabecular sinuses.

126 However, most of the plasma cells are present in those medullary sinuses that are found between the medullary cords (Weir and Stewart, 1997). In wistar rat haemolymph node, erythrocytes were observed only in the efferent lymphatic vessels (Nopajaroonsri et al., 1974), whereas in this study, erythrocytes were seen in both afferent and efferent lymphatics. This is in agreement with the results of Osman (1988) and Sharfee (1989) in camel mixed lymph nodes. The present observations agree with Osman (1988) and Sharfee (1989) that there are circumscribed areas near the capsule and trabeculae of the camel mixed lymph nodes. They are surrounded with flat discontinuous endothelial- like cells and contain erythrocytes, lymphocytes, macrophages and granulocytes. These areas communicate with the paratrabecular sinuses. The circumscribed areas also communicate either with the paratrabecular sinuses or with the terminal branches of the afferent lymphatic vessels. With advancing age, the erythrocytes increase in number substantially specially in the PMLN. The present study confirms the findings of Sharfee (1989) that in camel mixed lymph nodes, some lymphatic vessels open directly on the subcapsular sinuses. This indicates that erthrocytes may reach the node through the afferent lymphatics. Some nodes have no indentifiable hilus; arteries enter at different points. Some of these arteries are derived from a network of the capsule (Belz and Heat, 1995b). This is the most likely route of entry of erythrocytes in the camel mixed lymph nodes. However, Nopajaroonsri et al. (1974) reported that erthrocytes entered sinuses by crossing the wall of the postcapillary venules and capillaries and then passed through gaps in the wall of the sinuses. The present study is in agreement with Osman (1988) and Sharfee (1989) that in camel mixed lymph nodes, large numbers of red blood cells are observed in the subcapsular and paratrabecular sinuses. These sinuses are

127 connected to the circumscribed areas that are filled with blood. Red blood cells were also seen crossing the wall of the circumscribed areas from the surrounding interstitial spaces. This may lend support to the suggestion that erythrocytes get access to the afferent lymphatics through the lymphaticovenous communication or through connection between blood capillaries and the subcapsular and paratrabecular sinuses. The results of the present study confirm the suggestion of Abdel-Magied et al. (2001) that septal blood vessels may be a sourse for erythrocytes

IV.2.I.4. The Vascularization In the present study, there are many small blood vessels in the capsule and some of these vessels empty directly into the subcapsular sinus. The venules are classified into low endothelial venules, which contained a few intramural lymphocytes (Kawala and Schoefl, 1986) and high endothelial venules or postcapillary venules, which have many intraepithelial lymphocytes (Napajaroonsri et al., 1971; Kawala and Schoefl, 1986; Sharfee, 1989). The post-capillary venules are lined by cuboidal or columnar cells. This unusual endothelium allows lymphocytes to pass through the wall of the vessel but prevents the passage of fluid from the vessel to the parenchyma (Ross et al., 2000). The two types of venules are also observed in the present investigation.

128

IV.2.II.The Haemal Nodes IV.2.II.A.Gross Anatomy

The primary controversy about the haemal nodes has revolved around the question of whether they represent a modified lymph node or whether they are a separate and distinct form of lymphoid tissue. The present study confirms the findings of Folse et al. (1971) and Sharfee (1989) that their architecture and morphology is unique in comparison with other organized lymphoid organs. The haemal nodes have a dark red or dark brown colour. The nodes are interposed in the course of blood vessels and are usually embedded in adipose tissue (Folse et al., 1971; Dellmann and Brown, 1981; Sharfee, 1989). This is also true in the present observation. No lymphatic vessels were reported in the haemal nodes of the ox and other mammals (Folse et al., 1971; Banks, 1993). Turner (1969) reported that there were no afferent lymphatic vessels in the rat haemal node. Ezeasor and Singh (1988, 1990) and Fawcett (1994) reported the presence of efferent lymphatic vessels in the goat and rat respectively. The present study confirms the findings of Sharfee (1989) that both afferent and efferent lymphatic vessels are found and the afferent lymphatic vessels, on entering the node, are filled with blood. This may be an indication of direct connection between the blood vessels and the lymphatic vessels.

129

IV.2.II.B.Histology The present observation clearly confirms the earliar reports of Weller (1938), Folse et al. (1971), Dellmann and Brown (1981) and Sharfee (1989) that the capsule of the haemal node is composed of fibrous connective tissue. However, Folse et al. (1971), Dellmann and Brown (1981), Constantinescue (1988) and Banks (1993) reported the presence of smooth muscle fibres in the capsule of the node in the ox and some other mammals. As noted by previous investigators (Robertson, 1890; Sharfee, 1989), haemal nodes are generally embedded in adipose tissue. In contrast to the report of Clarkson (1891), no fat is found within the node itself. The present study confirms the findings of Folse et al. (1971) that underlying the capsule is a relatively large blood-filled sinus that accounts for the characteristic gross appearance of the bulk of the organ. Folse et al. (1971), Dellmann and Brown (1981) and Sharfee (1989) reported that the lining cells of the subcapsular sinuses, at the capsular side, appear to be endothelial and are continuous. This has been confirmed in the present study. The present study confirms the findings of Sharfee (1989) that there were circumscribed areas mainly found in the medulla and filled with blood. However, the medullary sinuses contained only a few red blood cells. This may indicate that continuous endothelial cells line the sinuses. Fenestrations through which small numbers of red blood cells pass in to the sinuses may be found. The present study also confirms the findings of Sharfee (1989) in the camel and Gargiulo, Pedeni, Faioli and Moriconi (1984) in sheep that continuous endothelial cells that line the medullary sinuses are also reported in haemal

130 nodes. However, in the ox and rat haemal nodes, the deeper sinusoids are lined with a discontinuous endothelial cells (Folse et al., 1971; Turner, 1971). Our present observation is in agreement with Sharfee (1989) that discontinuous endothelial cells surround the circumscribed areas. Our present observation confirms the findings of Ezeasor and Singh (1988) and Sharfee (1989) that the lumen of the medullary sinuses contains macrophages. Red blood cells are attached to the surface membrane or engulfed by the macrophages. The present investigation confirms the findings of Sharfee (1989) in the camel, and Folse et al. (1971) in the ox that the lymphoid tissue consists of cords, and nodules intermingled with the blood filled spaces and consist of loosely arranged cells mostly lymphocytes supported by reticular cells. Red blood cells are intermingled with lymphocytes inbetween the cords. The present investigation is not in agreement with the findings of Sharfee (1989) in the camel, Folse et al. (1971) in the ox and Dellman and Brown (1981) in the rat in that the nodules have typical germinal centres and the germinal centres are surrounded by a corona of small and darkly stained cells. The plasma cells are common in the germinal centres. The haemal nodes have direct blood supply to the sinusoidal system (Turner, 1969; Rhodin, 1974; Lorvik et al., 1983; Gargiulo et al., 1987). Some of the blood vessels in the capsule empty directly into the subcapsular sinuses and then terminate in the deep sinuses (Dellman and Brown, 1981). The results of this study confirm the findings of Sharfee (1989) that many red blood cells are found in the sinuses of the camel haemal nodes. These red blood cells reach the node through the afferent lymphatic vessels, which are filled with blood, and open directly into the subcapsular sinuses. The afferent lymphatic vessels terminate in the circumscribed areas. There may also be a direct contact

131 between blood vessels and subcapsular sinuses, circumscribed areas or the parenchyma because the amount of blood could not be attributed only to the afferent lymphatics. However, in goats there was no direct connection between the blood vessels and the sinuses or the parenchyma (Dellman and Brown, 1981).

132

IV.3. Electron Microscopy

The capsule, the trabeculae and the reticular cells form the stroma of the lymph nodes (Sorenson, 1960; Rhodin, 1974). In rats, the framework supporting the lymphoid parenchyma consists of collagen fibres accompanied by cytoplasmic prolongations of fibroblasts (Luk et al., 1973). The present study shows that the framework that supports the lymphoid parenchyma consists of reticular and elastic fibres. The results of this study confirm the findings of (Nopajroonsri et al., 1971; 1974) in the lymph nodes and haemolymph nodes of the rat that the capsule and trabeculae lack smooth muscle fibres. However, Rhodin (1974) claim that smooth muscle fibres are present in the capsule but absent in trabeculae.

The lymphocytes of wistar rat and camel nodes have round or oval indented nuclei, which show considerable variation in the size (Movat and Fernando, 1964; Nopajroonsri et al., 1971; Abdel-Magid, 1986; Sharfee, 1989; Osman et al., 1992). These results are similar to our observations. However, Abdel-Magid (1986) and Sharfee (1989) claim the presence of oblong nuclei. Peripheral heterochromatin and central nucleoli occasionally are seen and the cytoplasm contains ribosomes, mitochondria, Golgi apparatus and some scattered rough endoplasmic reticulum (Movat and Fernando, 1964; Nopajroonsri et al., 1971; Abdel-Magid, 1986; Sharfee, 1989; Osman et al.,

133 1992). This is similar to our results where the amount of the heterochromatin and the organelles in the cytoplasm depend on the size of the lymphocytes.

The electron microscopy revealed the biconcave disc shape of erythrocytes in all domestic animals studied (Kessel, 1998). The erythrocytes of the camel are elliptical in shape, nonnucleated and do not contain intracellular organelles. These findings are in agreement with those of Osman et al. (1992) and Omer (2003) and with the present investigation. The present investigation confirms the findings of Osman et al. (1992) and Omer (2003) that the neutrophil of the camel is characterized by a segmented nucleus that may have 3-5 lobes connected by a strand of nucleoplasm. Neutrophils often contain mitochondria, some membane-bound vesicles and Golgi complex. The cytoplasm contains a considerable number of membane-bound granules. These observations are similar to those in other domestic animals described by Dellmann and Brown (1981) and Banks (1993).

The present investigation is in agreement with the findings of Osman et al. (1992) and Omer (2003) that the most characteristic feature of acidophils examined by the electon microscope, is the presence of specific granules, which vary in size and have bars of crystalloids. The acidophil of the dog have no crystalloids in their granules whereas those of the cat have a core with myelin appearance (Dellmann and Brown, 1981; Banks, 1993). In human, the acidophil contains relatively less electron-lucent crystalloids (Birkitt et al., 1997).

The macrophages either have round nuclei with one or more indentation (Movat and Fernando, 1964; Nopajroonsri et al., 1971; Abdel-Magid, 1986) or have elongated nuclei (Rhodin, 1974). The present study confirms the findings

134 of Sharfee (1989) and Osman et al. (1992) that macrophages possess irregularly shaped nuclei and also the findings of Osman (1988) and Osman et al. (1992) that the surface display pseudopodia. The presence of a moderate amount of chromatin and a small nucleolus is reported in the camel (Abdel-Magid, 1986) and Albino rabbit (Movat and Fernando, 1964). The results of this study confirm the findings of Sharfee (1989) and Osman et al. (1992) in the camel that a few heterochromatin was seen in the macrophages. The results of this study confirm the findings of Abdel-Magid (1986) in the camel, Movat and Fernando (1964) in the rabbit and Nopajroonsri et al. (1971) in the rat that many vacuoles, lysosomal bodies, vesicles, small number of mitochondria and Golgi apparatus are found in the cytoplasm of the macrophages. Also the results of this study confirm the findings of Osman (1988), Sharfee (1989) and Osman et al. (1992) in the camel that the cytoplasm of the macrophages was loaded with lysosomal bodies, mitochondria, rough endoplasmic reticulum, free ribosomes and occasional golgi apparatus, in addition to the presence of the engulfed erythrocytes.

Plasma cells possess eccentric nuclei with dense peripheral chromatin in rabbits and hamsters (Movat and Fernando, 1962), rats (Nopajroonsri et al., 1971), sheep (Al-Bagdadi et al., 1986) and camels (Abdel-Magid, 1986; Sharfee, 1989; Osman et al., 1992). Plasma cells are either found singly or in groups (Nopajroonsri et al., 1971; Sharfee, 1989). The cytoplasm of the plasma cells contains rough endoplasmic reticulum (Nopajroonsri et al., 1971; Abdel- Magid, 1986; Osman, 1988; Sharfee, 1989; Osman et al., 1992), some mitochondria and free ribosomes (Sharfee, 1989; Osman et al., 1992). The Golgi apparatus is large in relation to the size of the cell in rats (Han, 1961), sheep (Al-Bagdadi et al., 1986) and camels (Osman et al., 1992). Similar

135 findings are found in the present results. However, in sheep phagocytosis of erythrocytes by plasma cells was reported by Al-Bagdadi et al. (1986). The results of this study confirm the findings of Abdel-Magid (1986) and Sharfee (1989) in the camel, Movat and Fernando (1964) in the rabbit and Nopajroonsri et al. (1971) in the rat in that reticular cells have elongated oval indented nuclei and herterochromatin is found at the periphery of the nucleus. The cytoplasm is rich in organelles, including rough endoplasmic reticulum, mitochondria, ribosomes and occasional Golgi apparatus. Also the results of this study confirm the findings of Abdel-Magid (1986) and Osman (1988) in the camel, Movat and Fernando (1964) in the rabbit and Rhodin (1974) humen in that branching cytoplasmic processes are present in the reticular cells.

136

IV.4.Morphometry

The present study shows that the mammary lymph node of the camel has a peculiar shape and is very large in size. The large size of this lymph node has already been reported by Osman (1988). Although it is not surprising to find a large node in so big an animal, it is interesting to note that all other lymph nodes of the camel are relatively small in size. Although the mammary lymph node of the camel is peculiar in shape and very large in size, yet the morphometric analysis showed similar results to those of other lymph nodes as reported by Abedel-Magied et al. (2001). For example in the present study, the parenchyma occupies about 82 % of the total volume of the node, whereas the connective tissue occupies about 18 % of the total volume of the node and that is similar to that reported in the same species in the parotid, mandibular and lateral retropharyngeal lymph nodes (Abedel- Magied et al., 2001).

137 The morphometric analysis has shown that the volume densities of the connective tissue, germinal centre, corona, diffuse lymphoid tissue, blood and lymph vessels and circumscribed areas are similar for the right and left nodes, and there is no significant difference between the right and left nodes in the relative volumes occupied by these components. This is in agreement with the result of Sarma et al. (2001) in the cervical nodes of Assam local goat. The volume densities of the stroma and parenchyma of the parotid, mandibular and retropharyngeal lymph nodes are similar (Abedel-Magied et al., 2001). The volume densities of the dense nodular lymphoid tissue is highest in the mandibular node, whereas that of the dense anodular tissue is highest in the lateral retropharyngeal node .The volume density of the diffuse lymphoid tissue is highest in the parotid lymph node. The camel has long been renowned for its ability to withstand diseases (Leese, 1927) and these unique lymph nodes may play a part in this phenomenon. The comparatively high volume density of the diffuse lymphoid tissue seen in this study may reflect the great ability of the camel lymph node to produce T-lymphocytes. Abbas et al. (1994) report that the diffuse lymphoid tissue is the site of T-lymphocytes production.

138

CONCLUSIONS

1. All components of blood (erythrocytes and leukocytes) are found inside the lymph nodes of camels. The presence of blood in lymph nodes increases their response to antigen.

2. The erythrocytes were very much distorted inside the lymph nodes. The significance of this needs further investigation.

3. The right and left mammary lymph nodes showed similar morphometric results.

139 4. A few lymph nodes, which are found in the domestic mammals are absent in the camel.

5. The amount of blood increases in the sinuses and circumscribed areas with age.

6. Some of the lymph nodes of the camel show clear lobulation in all ages.

7. The camel possesses only a few haemal nodes.

SUMMARY

1. Gross anatomical and histological study has been conducted on the lymph nodes in sixty camels (Camelus dromedarius) and haemal nodes in five camels from both sexes of different ages. 2. The ultrastructure of the parotid and mammary lymph nodes was investigated in three camels. 3. The morphometry of the mammary nodes was studied in three camels. The mammary lymph node was chosen because it is easily

140 accessible and it is the largest node when compared with the size of other lymph nodes. 4. The branching pattern of the arteries of mammary lymph node is studied in five camels by injuction of red Vinylite. 5. Analysis of the data revealed the presence of two groups of dromedary camel nodes: primary and secondary lymph nodes, and also some peculiarities in the lymph nodes anatomy. One of these peculiarities is the asymmetry in position, number and size of the right and left nodes in every lymphocentre of the SMLN more than of the PMLN. 6. The most significant difference between the camel lymph node and that of other domestic mammals is the existence of erythrocytes in the lymph sinuses and parenchyma of camel lymph node converting it to haemolymph node. 7. The age is a major factor in the involution of the lymphoid tissue in the camel lymph nodes shown by an increasing amount of the dark reddish patches on the surface of the node. 8. The PMLN showed distinct lobulation from outside more than in the SMLN. 9. The afferent lymphatics divided several times before entering the node at multiple points on the surface of the node through a shallow groove or deep invagination. 10. Some lymph nodes like the prefemoral and atrial nodes, which are present in most domestic mammals, are absent in the camel. 11. The lymph node is surrounded by a capsule, which enters the node at the hilus in the form of thick trabeculae dividing the node into many complete or incomplete lobes.

141 12. The amount of the connective tissue is more in PMLN than in SMLN and it is increased with advancing age. 13. The hilus varied in shape and size considerably in the different groups of lymph nodes and is easily distinguishable with advancing age. The simplest form of the hilus is seen in the SMLN whereas the large elongated node of the PMLN has more than one superficial hiluses. 14. Cortex and medulla are difficult to distingwish in the PMLN and are irregularly demarcated in the SMLN. Extensive cortex is found in the PMLN while extensive medulla is found in the SMLN. 15. The secondary nodules are located at the periphery of the lobules below the capsule and on either side of the trabeculae. The lymph nodule is consisted of a pale centrally area called a germinal centre and a periphery one called a corona. 16. The corona was in the form of half moons (demilunes) when the lymph nodule was located nearby a single trabecula or the capsule. The demilune corona was located facing the nearby trabecula or capsule. But if the lymph nodule was located between capsule and trabecula or between two or more trabeculae, the corona completely surrounded the germinal center. 17. The subcapsular and paratrabecular sinuses, which separate the parenchyma from the capsule and trabeculae respectively, are lined by a continuous layer of endothelial cells on the capsular and trabecular sides and by discontinuous layer on the parenchymal side.

142 18. In the PMLN, the cortical sinuses are larger than the medullary ones, while the medullary sinuses are more pronounced in the SMLN than in the PMLN. Both of them are lined by continuous layer of flat endothelial cells with basal lamina and supported by dense reticular and fine elastic fibres. 19. An important notable feature of camel lymph nodes is the presence of the circumscribed areas, which are found at the periphery of the lobules and are connected with the subcapsular and paratrabecular sinuses and with the terminal branches of the afferent lymphatics. They are filled with lymphocytes or contained blood and macrophages, according to the age. 20. The haemal nodes have a dark red or dark brown colour .The nodes are interposed along the blood vessels and usually embedded in adipose tissue. 21. In the haemal node, the cortex contained only a small number of primary lymph nodules. 22. In the haemal node, a large number of circumscribed areas are mainly found near the capsule and trabeculae, and also plenty in the medulla. They are filled with blood. 23. The ultrastructure demonstrated the presence of lymphocytes, erythrocytes, neutrophils, eosinophils, macrophages, plasma cells and reticular cells in the parotid and mammary lymph nodes. 24. There is no significant difference between the morphometric resultsof the right and left mammary lymph nodes of the camel. 25. The mean absulute volume of the right mammary lymph node is 51.33 cm.³ ±10.26 (SD), whereas the mean absulute volume of the left mammary lymph node is 51.33 cm.³ ±17.00 (SD).

143 26. The parenchyma of the right mammary lymph node accounts for about 83.14% of the total volume of the node, and the connective tissue occupies about 16.86%. 27. The parenchyma of the left mammary lymph node accounts for about 81.82% of the total volume of the node, and the connective tissue occupies about 18.18%.

144

ﺍﻟﻤﻠﺨﺹ

1. ﺃﺠﺭﻴﺕ ﻫﺫﻩ ﺍﻟﺩﺭﺍﺴﺔ ﻟﻠﺘﻌﺭﻑ ﻋﻠﻰ ﺍﻟﺴﻤﺎﺕ ﺍﻟﺘﺸﺭﻴﺤﻴﺔ ﻭﺍﻟﺒﻨﻴﺔ ﺍﻟﻨﺴﻴﺠﻴﺔ ﻟﻠﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﻓﻲ ﺴﺘﻴﻥ ﻤﻥ ﺍﻹﺒل ﻭﺃﻴﻀﺎ ﻟﻠﻌﻘﺩ ﺍﻟﺩﻤﻭﻴﺔ ﻤﻥ ﺍﻟﺠﻨﺴﻴﻥ ﺒﻤﺨﺘﻠﻑ ﺍﻷﻋﻤﺎﺭ. 2. ﺘﻤﺕ ﺩﺭﺍﺴﺔ ﺍﻟﻌﻘﺩﺘﻴﻥ ﺍﻟﻠﻤﻔﺎﻭﻴﺘﻴﻥ ﺍﻟﻨﻜﻔﻴﺔ ﻭﺍﻟﺜﺩﻴﻴﺔ ﺒﺎﻟﻤﺠﻬﺭ ﺍﻹﻟﻜﺘﺭﻭﻨﻲ ﻓﻲ ﺜﻼﺜﺔ ﻤﻥ ﺍﻹﺒل. 3. ﺘﻤﺕ ﺩﺭﺍﺴﺔ ﺍﻟﻘﻴﺎﺱ ﺍﻟﺸﻜﻠﻲ (ﺍﻟﻤﻭﺭﻓﻭﻤﺘﺭﻱ) ﻓﻲ ﺍﻟﻌﻘﺩﺓ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻟﺜﺩﻴﻴﺔ ﻓﻘﻁ ﻓﻲ ﺜﻼﺜﺔ ﻤﻥ ﺍﻹﺒل ﻭ ﺫﻟﻙ ﻟﺴﻬﻭﻟﺔ ﺍﻟﺤﺼﻭل ﻋﻠﻴﻬﺎ ﻭﻜﺒﺭ ﺤﺠﻤﻬﺎ ﻤﻘﺎﺭﻨﺔ ﺒﺒﻘﻴﺔ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ. 4. ﺍﻟﺘﻔﺭﻋﺎﺕ ﺍﻟﺸﺭﻴﺎﻨﻴﺔ ﻟﻠﻌﻘﺩﺓ ﺍﻟﺜﺩﻴﻴﺔ ﺩﺭﺴﺕ ﻓﻰ ﺨﻤﺱ ﻤﻥ ﺍﻹﺒل ﺒﺎﻟﺤﻘﻥ ﺒﻤﺎﺩﺓ ﺍﻟﻔﻨﻼﻴﺕ ﺍﻟﺤﻤﺭﺍﺀ. 5. ﺃﻅﻬﺭﺕ ﺍﻟﺩﺭﺍﺴﺔ ﻭﺠﻭﺩ ﻨﻭﻋﻴﻥ ﻤﻥ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﻓﻲ ﺍﻹﺒل: ﻋﻘﺩ ﺃﻭﻟﻴﺔ ﻭﺜﺎﻨﻭﻴﺔ ﻟﻤﻔﺎﻭﻴﺔ ﻤﺨﺘﻠﻁﺔ، ﻭﺃﻴﻀﺎ ﺃﻭﻀﺤﺕ ﺍﻟﺩﺭﺍﺴﺔ ﻭﺠﻭﺩ ﻋﺩﺓ ﺼﻔﺎﺕ ﺘﺸﺭﻴﺤﻴﺔ ﻤﻤﻴﺯﺓ ﻟﻬﺫﻩ ﺍﻟﻌﻘﺩ. ﺇﺤﺩﻯ ﻫﺫﻩ ﺍﻟﺼﻔﺎﺕ ﺘﺘﻤﺜل ﻓﻲ ﻋﺩﻡ ﺘﻁﺎﺒﻕ ﺍﻷﺤﺠﺎﻡ ﻭﺍﻷﻋﺩﺍﺩ ﻭﺍﻟﻤﻭﺍﻗﻊ ﻟﻜل ﻤﺭﻜﺯ ﻟﻤﻔﺎﻭﻯ ﻤﺎ ﺒﻴﻥ ﺍﻟﺠﻬﺔ ﺍﻟﻴﻤﻨﻰ ﻭﺍﻟﻴﺴﺭﻯ ﻟﻠﺤﻴﻭﺍﻥ ﻟﻠﻌﻘﺩ ﺍﻟﺜﺎﻨﻭﻴﺔ ﺍﻟﻤﺨﺘﻠﻁﺔ ﺃﻜﺜﺭ ﻤﻨﻬﺎ ﻟﻠﻌﻘﺩ ﺍﻷﻭﻟﻴﺔ ﺍﻟﻤﺨﺘﻠﻁﺔ . 6. ﻤﻥ ﺃﻫﻡ ﺍﻟﻔﺭﻭﻗﺎﺕ ﺒﻴﻥ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﻓﻰ ﺍﻹﺒل ﻭﻓﻰ ﺍﻟﺜﺩﻴﺎﺕ ﺍﻟﻤﺴﺘﺄﻨﺴﺔ ﺍﻵﺨﺭﻯ ﻭﺠﻭﺩ ﻜﺭﻴﺎﺕ ﺩﻡ ﺤﻤﺭﺍﺀ ﻓﻰ ﺍﻟﺠﻴﻭﺏ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﻭﺍﻟﻨﺴﻴﺞ ﺍﻟﺤﺸﻭﻯ ﻓﻰ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﻓﻰ ﺍﻹﺒل ﻟﺘﺘﺤﻭل ﺍﻟﻰ ﻋﻘﺩ ﺩﻤﻭﻴﺔ ﻟﻤﻔﺎﻭﻴﺔ. 7. ﺍﻟﻌﻤﺭ ﻋﺎﻤل ﺭﺌﻴﺴﻰ ﻓﻰ ﺍﻟﺘﺤﻭﺭﺍﺕ ﺍﻟﺘﻰ ﺘﺤﺩﺙ ﻓﻰ ﺍﻟﻨﺴﻴﺞ ﺍﻟﻠﻤﻔﺎﻭﻱ ﻓﻰ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﻭﻴﺘﻀﺢ ﺫﻟﻙ ﺒﺯﻴﺎﺩﺓ ﻓﻰ ﻜﻤﻴﺔ ﺍﻟﻠﻁﺨﺎﺕ ﺩﺍﻜﻨﺔ ﺍﻹﺤﻤﺭﺍﺭ ﻋﻠﻰ ﺴﻁﺤﻬﺎ.

145 8. ﺘﺘﻤﻴﺯ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻟﻤﺨﺘﻠﻁﺔ ﺍﻷﻭﻟﻴﺔ ﺒﺘﻔﺼﺹ ﻭﺍﻀﺢ ﻋﻠﻰ ﺴﻁﺤﻬﺎ ﺍﻟﺨﺎﺭﺠﻰ ﺃﻜﺜﺭ ﻭﻀﻭﺤﺎ ﻤﻥ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻟﻤﺨﺘﻠﻁﺔ ﺍﻟﺜﺎﻨﻭﻴﺔ. 9. ﺍﻷﻭﻋﻴﺔ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻟﻭﺍﺭﺩﺓ ﺘﺘﻔﺭﻉ ﻋﺩﺓ ﻤﺭﺍﺕ ﻗﺒل ﺇﺨﺘﺭﺍﻗﻬﺎ ﻟﺴﻁﺢ ﺍﻟﻌﻘﺩﺓ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺨﻼل ﺃﺨﺎﺩﻴﺩ ﻀﺤﻠﺔ ﺃﻭ ﺇﻨﺨﺴﺎﻓﺎﺕ ﻋﻤﻴﻘﺔ ﻓﻰ ﻋﺩﺓ ﻤﻨﺎﻁﻕ ﻤﻥ ﺍﻟﻤﺤﻔﻅﺔ. 10. ﺃﻅﻬﺭﺕ ﺍﻟﺩﺭﺍﺴﺔ ﻏﻴﺎﺏ ﺒﻌﺽ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﻤﺜل ﺍﻟﻌﻘﺩﺘﻴﻥ ﺃﻤﺎﻡ ﺍﻟﻔﺨﺫﻴﺔ ﻭﺍﻟﺒﻬﻭﻴﺔ ﻓﻰ ﺍﻹﺒل؛ ﺘﻠﻙ ﺍﻟﻌﻘﺩ ﺘﻭﺠﺩ ﻓﻰ ﺍﻟﺜﺩﻴﺎﺕ ﺍﻟﻤﻨﺯﻟﻴﺔ ﺍﻷﺨﺭﻯ. 11. ﺘﺤﺎﻁ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺒﻤﺤﻔﻅﺔ ﺘﺨﺘﺭﻕ ﻤﻨﻁﻘﺔ ﺍﻟﺴﺭﺓ ﻓﻰ ﺸﻜل ﺤﻭﺍﺠﺯ ﺴﻤﻴﻜﺔ ﻟﺘﻘﺴﻡ ﺍﻟﻌﻘﺩﺓ ﺍﻟﻰ ﻓﺼﻭﺹ. 12. ﻜﻤﻴﺔ ﺍﻟﻨﺴﻴﺞ ﺍﻟﻀﺎﻡ ﻓﻰ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻟﻤﺨﺘﻠﻁﺔ ﺍﻷﻭﻟﻴﺔ ﺃﻜﺜﺭ ﻤﻤﺎ ﻫﻭ ﻤﻭﺠﻭﺩ ﻓﻰ ﺍﻟﺜﺎﻨﻭﻴﺔ ﻭﺘﺯﺩﺍﺩ ﻜﻤﻴﺔ ﺍﻟﻨﺴﻴﺞ ﺍﻟﻀﺎﻡ ﺒﺘﻘﺩﻡ ﺍﻟﻌﻤﺭ. 13. ﺍﻟﺴﺭﺓ ﺘﺨﺘﻠﻑ ﺒﺎﺨﺘﻼﻑ ﺍﻟﻤﺠﻤﻭﻋﺎﺕ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﻭﻴﺴﻬل ﺘﻤﻴﻴﺯﻫﺎ ﺒﺘﻘﺩﻡ ﺍﻟﻌﻤﺭ . ﺃﺒﺴﻁ ﺸﻜل ﻟﻠﺴﺭﺓ ﻴﻭﺠﺩ ﻓﻰ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻟﺜﺎﻨﻭﻴﺔ ﺍﻟﻤﺨﺘﻠﻁﺔ ﺒﻴﻨﻤﺎ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻷﻭﻟﻴﺔ ﺍﻟﻤﺨﺘﻠﻁﺔ ﺍﻟﻜﺒﻴﺭﺓ ﺍﻟﻤﺘﻁﺎﻭﻟﺔ ﺘﺘﻤﻴﺯ ﺒﻭﺠﻭﺩ ﺃﻜﺜﺭ ﻤﻥ ﺴﺭﺓ ﺴﻁﺤﻴﺔ. 14. ﻴﺼﻌﺏ ﺍﻟﺘﻤﻴﻴﺯ ﺒﻴﻥ ﺍﻟﻘﺸﺭﺓ ﻭﺍﻟﻨﺨﺎﻉ ﻓﻰ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻷﻭﻟﻴﺔ ﺤﻴﺙ ﻴﻭﺠﺩﺍﻥ ﻋﻠﻰ ﺸﻜل ﻤﻨﺎﻁﻕ ﻏﻴﺭ ﻤﻨﺘﻅﻤﺔ ﺍﻟﻤﻌﺎﻟﻡ . ﺘﻭﺠﺩ ﺍﻟﻘﺸﺭﺓ ﺒﻜﻤﻴﺔ ﺃﻜﺒﺭ ﻓﻰ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻷﻭﻟﻴﺔ ﺍﻟﻤﺨﺘﻠﻁﺔ ﺒﻴﻨﻤﺎ ﻴﻭﺠﺩ ﺍﻟﻨﺨﺎﻉ ﺒﺸﻜل ﺃﻜﺒﺭ ﻓﻰ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻟﺜﺎﻨﻭﻴﺔ ﺍﻟﻤﺨﺘﻠﻁﺔ. 15. ﺍﻟﻌﻘﻴﺩﺍﺕ ﺍﻟﺜﺎﻨﻭﻴﺔ ﺘﻭﺠﺩ ﻋﻠﻰ ﻤﺤﻴﻁ ﺍﻟﻔﺼﻴﺼﺎﺕ، ﺘﺤﺕ ﺍﻟﻐﻼﻑ ﻭﻋﻠﻰ ﺠﺎﻨﺒﻲ ﺍﻟﺤﻭﺍﺠﺯ. ﺘﺘﻜﻭﻥ ﺍﻟﻌﻘﻴﺩﺓ ﻤﻥ ﻤﻨﻁﻘﺔ ﻤﺭﻜﺯﻴﺔ ﺸﺎﺤﺒﺔ ﺍﻟﻠﻭﻥ ﺘﺴﻤﻰ ﺍﻟﻤﺭﻜﺯ ﺍﻟﺠﺭﺜﻭﻤﻰ ﻭﻤﻨﻁﻘﺔ ﻤﺤﻴﻁﻴﺔ ﺘﺴﻤﻰ ﺍﻟﻤﻨﻁﻘﺔ ﺍﻟﺘﺎﺠﻴﺔ. 16. ﺘﻜﻭﻥ ﺍﻟﻤﻨﻁﻘﺔ ﺍﻟﺘﺎﺠﻴﺔ ﻋﻠﻰ ﺸﻜل ﻨﺼﻑ ﻫﻼﻟﻰ ﻋﻨﺩﻤﺎ ﺘﺘﻭﻀﻊ ﺍﻟﻌﻘﻴﺩﺓ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺒﺠﻭﺍﺭ ﺤﺎﺠﺯ ﻭﺍﺤﺩ ﺃﻭ ﺍﻟﻤﺤﻔﻅﺔ ﻭﻋﻨﺩﻫﺎ ﺘﻜﻭﻥ ﺍﻟﻤﻨﻁﻘﺔ ﺍﻟﺘﺎﺠﻴﺔ ﻤﻭﺍﺠﻬﺔ

146 ﻟﻬﺫﺍ ﺍﻟﺤﺎﺠﺯ ﺃﻭ ﺍﻟﻤﺤﻔﻅﺔ. ﺃﻤﺎ ﻋﻨﺩ ﻭﺠﻭﺩ ﺍﻟﻌﻘﻴﺩﺓ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺒﻴﻥ ﺍﻟﻤﺤﻔﻅﺔ ﻭﺤﺎﺠﺯ ﺃﻭ ﺒﻴﻥ ﺤﺎﺠﺯﻴﻥ ﺃﻭ ﺃﻜﺜﺭ ﺘﻜﻭﻥ ﺍﻟﻤﻨﻁﻘﺔ ﺍﻟﺘﺎﺠﻴﺔ ﻤﺤﻴﻁﺔ ﺘﻤﺎﻤﺎ ﺒﺎﻟﻤﺭﻜﺯ ﺍﻟﺠﺭﺜﻭﻤﻰ. 17. ﺍﻟﺠﻴﻭﺏ ﺘﺤﺕ ﺍﻟﻐﻼﻑ ﻭﺠﻨﻴﺏ ﺍﻟﺤﻭﺍﺠﺯ ﻭﺍﻟﺘﻰ ﺘﻔﺼل ﺍﻟﻐﻼﻑ ﻭﺍﻟﺤﻭﺍﺠﺯ ﻋﻥ ﺍﻟﻤﺘﻥ ﻋﻠﻰ ﺍﻟﺘﻭﺍﻟﻰ ﺘﺒﻁﻥ ﺒﻁﺒﻘﺔ ﻤﺘﺼﻠﺔ ﻤﻥ ﺍﻟﺨﻼﻴﺎ ﺍﻟﺒﻁﺎﻨﻴﺔ ﻓﻰ ﺠﺎﻨﺏ ﺍﻟﻐﻼﻑ ﻭﺍﻟﺤﻭﺍﺠﺯ ﻭﺒﻁﺒﻘﺔ ﻏﻴﺭ ﻤﺘﺼﻠﺔ ﻓﻰ ﺠﺎﻨﺏ ﺍﻟﻨﺴﻴﺞ ﺍﻟﺤﺸﻭﻯ. 18. ﺍﻟﺠﻴﻭﺏ ﺍﻟﻘﺸﺭﻴﺔ ﻓﻰ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻷﻭﻟﻴﺔ ﺍﻟﻤﺨﺘﻠﻁﺔ ﺃﻜﺒﺭ ﻤﻥ ﺍﻟﺠﻴﻭﺏ ﺍﻟﻨﺨﺎﻋﻴﺔ ﺒﻴﻨﻤﺎ ﺍﻟﺠﻴﻭﺏ ﺍﻟﻨﺨﺎﻋﻴﺔ ﺃﻭﻀﺢ ﻓﻰ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻟﺜﺎﻨﻭﻴﺔ ﺍﻟﻤﺨﺘﻠﻁﺔ ﻤﻥ ﻤﺜﻴﻼﺘﻬﺎ ﻓﻰ ﺍﻷﻭﻟﻴﺔ ﻭﻜﻼ ﺍﻟﻨﻭﻋﻴﻥ ﻴﺒﻁﻥ ﺒﻁﺒﻘﺔ ﻤﺘﺼﻠﺔ ﻤﻥ ﺍﻟﺨﻼﻴﺎ ﺍﻟﺒﻁﺎﻨﻴﺔ ﺍﻟﻤﻔﻠﻁﺤﺔ ﻤﻊ ﻏﺸﺎﺀ ﻗﺎﻋﺩﻯ ﻤﺩﻋﻡ ﺒﻁﺒﻘﺔ ﻜﺜﻴﻔﺔ ﻤﻥ ﺍﻷﻟﻴﺎﻑ ﺍﻟﺸﺒﻜﻴﺔ ﻭﺍﻟﻤﺭﻨﺔ. 19. ﻤﻥ ﺃﻫﻡ ﻤﻤﻴﺯﺍﺕ ﺍﻟﻌﻘﺩ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﻓﻰ ﺍﻹﺒل ﻫﻭ ﻭﺠﻭﺩ ﻤﺴﺎﺤﺎﺕ ﺩﺍﺌﺭﻴﺔ ﻤﺤﺩﺩﺓ ﻋﻠﻰ ﺃﻁﺭﺍﻑ ﺍﻟﻔﺼﻴﺼﺎﺕ ﻭﺘﺘﺼل ﺒﺎﻟﺠﻴﻭﺏ ﺘﺤﺕ ﺍﻟﻐﻼﻑ ﻭﺠﻨﻴﺏ ﺍﻟﺤﻭﺍﺠﺯ ﻭﺍﻟﺘﻔﺭﻋﺎﺕ ﺍﻟﻨﻬﺎﺌﻴﺔ ﻟﻸﻭﻋﻴﺔ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺍﻟﻭﺍﺭﺩﺓ ﻭﺘﻤﺘﻠﺊ ﺒﺎﻟﺨﻼﻴﺎ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ ﺒﺎﻹﻀﺎﻓﺔ ﺍﻟﻰ ﺍﻟﺩﻡ ﻭﺍﻟﺨﻼﻴﺎ ﺍﻟﺒﻠﻌﻤﻴﺔ ﺤﺴﺏ ﻋﻤﺭ ﺍﻟﺤﻴﻭﺍﻥ. 20. ﺍﻟﻌﻘﺩ ﺍﻟﺩﻤﻭﻴﺔ ﻋﺒﺎﺭﺓ ﻋﻥ ﻋﻘﺩ ﺤﻤﺭﺍﺀ ﺃﻭ ﺒﻨﻴﺔ ﺩﺍﻜﻨﺔ ﺍﻟﻠﻭﻥ ﺘﻭﺠﺩ ﻓﻰ ﻤﺴﺎﺭ ﺍﻷﻭﻋﻴﺔ ﺍﻟﺩﻤﻭﻴﺔ ﻭﻤﺤﺎﻁﺔ ﺒﻨﺴﻴﺞ ﺩﻫﻨﻰ. 21. ﺘﺤﺘﻭﻯ ﺍﻟﻘﺸﺭﺓ ﻓﻰ ﺍﻟﻌﻘﺩﺓ ﺍﻟﺩﻤﻭﻴﺔ ﻋﻠﻰ ﺃﻋﺩﺍﺩ ﻗﻠﻴﻠﺔ ﻤﻥ ﺍﻟﻌﻘﻴﺩﺍﺕ ﺍﻹﺒﺘﺩﺍﺌﻴﺔ ﺒﻴﻨﻤﺎ ﺍﻟﺜﺎﻨﻭﻴﺔ ﻏﻴﺭ ﻤﻭﺠﻭﺩﺓ. 22. ﺘﻭﺠﺩ ﺃﻋﺩﺍﺩ ﻜﺒﻴﺭﺓ ﻤﻥ ﺍﻟﻤﺴﺎﺤﺎﺕ ﺍﻟﺩﺍﺌﺭﻴﺔ ﺍﻟﻤﺤﺩﺩﺓ ﺒﺼﻭﺭﺓ ﻤﻜﺜﻔﺔ ﺒﺠﻭﺍﺭ ﺍﻟﻐﻼﻑ ﻭﺍﻟﺤﻭﺍﺠﺯ ، ﻭﺃﻴﻀﺎ ﻓﻰ ﺍﻟﻠﺏ ﻭﺘﻜﻭﻥ ﻤﻤﺘﻠﺌﺔ ﺒﺎﻟﺩﻡ. 23. ﺘﻤﺕ ﺩﺭﺍﺴﺔ ﺍﻟﻌﻘﺩﺘﻴﻥ ﺍﻟﻠﻤﻔﺎﻭﻴﺘﻴﻥ ﺍﻟﻨﻜﻔﻴﺔ ﻭﺍﻟﺜﺩﻴﺔ ﺒﺎﺴﺘﺨﺩﺍﻡ ﺍﻟﻤﺠﻬﺭ ﺍﻹﻟﻜﺘﺭﻭﻨﻲ ﻭﺘﻡ ﺍﻟﺘﺭﻜﻴﺯ ﻋﻠﻰ ﺍﻹﺨﺘﻼﻓﺎﺕ ﺍﻟﺭﺌﻴﺴﻴﺔ ﺍﻟﻤﻤﻴﺯﺓ ﻟﻜل ﻤﻥ ﻜﺭﻴﺎﺕ ﺍﻟﺩﻡ ﺍﻟﺤﻤﺭﺍﺀ ﻭﺍﻟﺨﻼﻴﺎ ﺍﻟﻠﻤﻔﺎﻭﻴﺔ، ﺍﻟﻤﺘﻌﺎﺩﻟﺔ، ﺍﻟﺤﻤﻀﻴﺔ، ﺍﻟﺒﻠﻌﻤﻴﺔ، ﺍﻟﺒﻠﺯﻤﻴﺔ ﻭﺍﻟﺸﺒﻜﻴﺔ.

147 24. ﻻ ﻴﻭﺠﺩ ﻓﺭﻕ ﻭﺍﻀﺢ ﻓﻰ ﺍﻟﻨﺘﺎﺌﺞ ﺍﻟﻘﻴﺎﺴﻴﺔ ﺍﻟﺸﻜﻠﻴﺔ (ﺍﻟﻤﻭﺭﻓﻭﻤﺘﺭﻴﺔ) ﺒﻴﻥ ﺍﻟﻌﻘﺩﺘﻴﻥ ﺍﻟﻠﻤﻔﺎﻭﻴﺘﻴﻥ ﺍﻟﺜﺩﻴﺘﻴﻥ ﺍﻟﻴﻤﻨﻰ ﻭﺍﻟﻴﺴﺭﻯ ﻓﻰ ﺍﻹﺒل. 25. ﻤﺘﻭﺴﻁ ﺍﻟﺤﺠﻡ ﻟﻠﻌﻘﺩﺓ ﺍﻟﺜﺩﻴﻴﺔ ﺍﻟﻴﻤﻨﻰ ﻫﻭ (cm.³ ±10.26 (SD 51.33 ﺒﻴﻨﻤﺎ ﻴﻜﻭﻥ ﻓﻰ ﺍﻟﻌﻘﺩﺓ ﺍﻟﺜﺩﻴﻴﺔ ﺍﻟﻴﺴﺭﻯ (cm.³ ±17.00 (SD 51.33. 26. ﻤﺘﻥ ﺍﻟﻌﻘﺩﺓ ﺍﻟﺜﺩﻴﻴﺔ ﺍﻟﻴﻤﻨﻰ ﻴﺸﻜل ﺘﻘﺭﻴﺒﺎ %83.14 ﻤﻥ ﺤﺠﻡ ﺍﻟﻌﻘﺩﺓ ﺍﻟﻜﻠﻰ ﺒﻴﻨﻤﺎ ﻴﺸﻜل ﺍﻟﻨﺴﻴﺞ ﺍﻟﻀﺎﻡ ﺤﻭﺍﻟﻰ16.86% . 27. ﻤﺘﻥ ﺍﻟﻌﻘﺩﺓ ﺍﻟﺜﺩﻴﻴﺔ ﺍﻟﻴﺴﺭﻯ ﻴﺸﻜل ﺘﻘﺭﻴﺒﺎ %81.82 ﻤﻥ ﺤﺠﻡ ﺍﻟﻌﻘﺩﺓ ﺍﻟﻜﻠﻰ ﺒﻴﻨﻤﺎ ﻴﺸﻜل ﺍﻟﻨﺴﻴﺞ ﺍﻟﻀﺎﻡ ﺤﻭﺍﻟﻰ 18.18% .

148

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FIGURE

Figure 1: A diagram showing some of the lymph nodes of the camel.

174 1. The parotid node 2. The mandibular node 3. The medial retropharyngeal node 4. The cranial deep cervical nodes 5. The middle deep cervical nodes 6. The caudal deep cervical nodes 7. The dorsal superficial cervical node 8. The ventral superficial cervical node 9. The intercostal nodes 10. The thoracic aortic nodes 11. The cranial mediastinal lymph nodes 12. The middle mediastinal lymph nodes 13. The caudal mediastinal lymph nodes 14. The bronchial lymph nodes 15. The lumbar aortic lymph nodes 16. The renal lymph nodes 17. The superficial inguinal lymph nodes 18. The tuberal lymph nodes 19. The gastric lymph nodes

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Figure 2: A diagram to indicate the locations of the parotid and mandibular nodes. 1-The parotid node 2-The mandibular node 3-The parotid salivary gland 4-The masseter muscles 5-The masseter artery 6-The facial nerve 7-The linguofacial vein 8-The lingual vein 9-The facial vein

Figure 3: A diagram showing the location of the caudal mediastinal lymph node (1). 2. Aorta 3. Thoracic oesophagus Note that the medial part of the node is wider than the cranial and caudal parts.

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Figure 4: The shape of the parotid lymph nodes changes with advancing age. The colour of the lymph nodes in young animals is pink (1). With advancing age, irregular dark reddish patches appear on the surfaces of the node (2&3). These patches, in old animals, fused together and the colour of the node becomes dark red (4&5).

Figure 5: A photograph showing many differences between right (R) and left (L) parotid nodes, which become clearer with advancing age.

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Figure 6: A photograph showing the right middle deep cervical lymph node (arrows) 1. Oesophagus 2. Trachea

Figure 7: A cast showing the arterial branches of the mammary lymph node 1. The external pudendal artery 2. Branch of the external pudendal artery 3. The major nodal arteries 4. Trabecular arteries

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Figure 8: A photograph showing the mammary (left) and the parotid lymph nodes (right). The former is quite big when compared to the latter in the same animal. Note the external lobulation of the mammary lymph node. The hilus is elongated and situated in a long groove (arrows).

Figure 9: A higher magnification from figure 8 showing the afferent lymphatic vessel pierces the node and is full of blood. The lobules have different colour as seen from the surface.

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Figure 10: A photomicrograph of the parotid lymph node from young animal showing the fibroconnective tissue thick capsule (C) and thin trabeculae (T) extending from the capsule into the parenchyma of the node. H&E stain. X40.

Figure 11: A photomicrograph of the parotid lymph node from a young animal showing thick trabeculae (Tı) extending from the hilus (H)

and thin trabeculae (T2). The trabeculae divide the node into lobes and lobules. The node is a partially mixed node. H&E stain. X40.

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Figure 12: A photomicrograph of the retropharyngeal lymph node from a young animal. The outer surface of the capsule (C) merges with the surrounding adipose tissue (A). The capsule contains large bundles of collagen fibres Van Gesson’s stain. X 250.

Figure 13: A photomicrograph of the retropharyngeal lymph node from a young animal. Elastic fibres of the capsule (C) are shown as wavy longitudinal fibres (arrows). The outer part of the capsule contains more elastic fibres than the inner part. SS: subcapsular sinuses CS: cortical sinuses Verhoeff ’s stain. X250.

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Figure 14: A photomicrograph of the ventral superficial cervical lymph node from adult animal The elastic fibres (arrows) of the trabeculae are concentrated at the core of the trabeculae. The trabeculae are completely surrounded by endothelial cells (E) of the paratrabecular sinuses (PS). GC: germinal centre C: corona Orcein’s stain. X250.

Figure 15: A photomicrograph of the dorsal superficial cervical lymph node from adult animal showing thick trabeculae (T) containing a few reticular fibres and were completely surrounded by the paratrabecular sinuses (PS) that are traversed by a dense network of reticular fibres (arrows). Gomori’s silver stain. X100.

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Figure 16: A photomicrograph of the tuberal lymph node from a young animal showing secondary nodules located at the periphery of the lobules on either side of the trabeculae (T). The demilunes corona (C) face the nearby trabeculae. Note the germinal centres (GC). H&E stain. X40.

Figure 17: A photomicrograph of the retropharyngeal lymph node from a young animal. The reticular fibres are found around the blood vessels (BV), around the lymph nodule (N) and inside the nodule (arrows). Gomori’s silver stain. X100.

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Figure 18: A photomicrograph of the retropharyngeal lymph node from adult animal. Some lymph nodules are fused together. Secondary nodules with large pale germinal centre (GC) and dark corona (C) are located below the capsule and on either side of the trabeculae and possess Van Gieson’s stain. X40.

Figure 19: A higher magnification of figure 18 showing the close association of the lymph nodules with the paratrabecular sinuses (PS). Note the pale staining germinal centre (GC) and the dark corona (C). Van Gieson’s stain. X250.

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Figure 20: A photomicrograph of the pancreaticoduodenal lymph node from adult animal. Large (L), medium-sized (M) and small lymphocytes (S) are found in the germinal centre, whereas the corona is packed with small lymphocytes and a few number of medium-sized lymphocytes. Verhoeff ’s stain. X1000.

Figure 21: A photomicrograph of the retropharyngeal lymph node from a young animal. A longitudinal section of capillary (arrows) enters a secondary nodule. Note the germinal centre (GC), the corona (C) and the diffuse lymphoid tissue (D) around the lymph nodule. H&E stain. X250.

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Figure 22: A photomicrograph of the retropharyngeal lymph node from adult animal showing dense (D) and light (L) diffuse lymphoid tissue, lymph nodule (N), trabeculae (T) and paratrabecular sinuses (PS). H&E stain. X100.

Figure 23: A photomicrograph of the mammary lymph node from adult animal. The medulla with an extensive branched trabeculae (MT) and small blood vessels (BV) are indicated. Note the cross sections of the cortical trabeculae (CT) and the lymph nodules (N). H&E stain. X100.

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Figure 24: A photomicrograph of the parotid lymph node from a young animal. The medulla possesses a few reticular fibres. Gomori’s silver stain. X250.

Figure 25: A photomicrograph of the parotid lymph node from adult animal showing dense reticular fibres in the medulla, especially around blood vessels (BV), and less in the cortex (C). Gomori’s silver stain. X250.

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Figure 26: A photomicrograph of the dorsal superficial cervical lymph node from adult animal. An afferent lymphatic vessel (AL) opens (arrow) directly into the cortical sinuses (CS). H&E stain. X250.

Figure 27: A photomicrograph of the retropharyngeal lymph node from a young animal. Note: • Longitudinal section of an afferent lymphatic vessel (AL) provided with valve (arrows). • Branch of an afferent lymphatic (BA) opens directly into the cortical sinuses (CS). H&E stain. X250.

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Figure 28: A photomicrograph of the retropharyngeal lymph node from adult animal showing a continuous layer of the endothelium (arrows) of the subcapsular sinuses on the capsular side (C) and a discontinuous layer on the parenchymal side. Note the granulocytes (G) in the subcapsular sinuses (SS). H&E stain. X1000.

Figure 29: A photomicrograph of the retropharyngeal lymph node from a young animal. The reticular fibres (arrows) originate from the fibrous capsule (C), traverse the subcapsular sinuses (S) and continue with the reticular fibres of the cortex. Gomori’s silver stain. X500.

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Figure 30: A photomicrograph of the retropharyngeal lymph node from a young animal showing the terminal branches (B) of the afferent lymphatic that contain lymph and open directly into the subcapsular sinuses (arrows). H&E stain. X250.

Figure 31: Retropharyngeal lymph node from old animal showing the presence of blood in the subcapsular sinuses (SS), paratrabecular sinuses (PS) and in the parenchyma (P). Note: • The cortical sinuses (CS) are distinct and lined by continuous endothelial cells. • The large corona (C) and small germinal centre (GC). H&E stain. X250.

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Figure 32: A photomicrograph of the retropharyngeal lymph node from a young animal. Circumscribed areas (CA) are found at the periphery of the node and the subcapsular sinuses (SS) open into these areas. Elastic fibres (arrows) are found in the capsule (C). Verhoeff ’s stain. X250.

Figure 33: A photomicrograph of the mandibular lymph node from adult animal. Note: • The trabeculae contain trabecular lymphatic vessels (TV).

209 • The reticular fibres (arrows) traverse the paratrabecular sinuses and continue with the reticular fibres of the parenchyma. Gomori’s silver stain. X100.

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Figure 34: A photomicrograph of the retropharyngeal lymph node from adult animal showing several circumscribed areas (CA) at the periphery of the node. Some of them are filled with blood. Note the capsule (C) and the lymph nodule (N). H&E stain. X100.

Figure 35: A photomicrograph of the retropharyngeal lymph node from a young animal. Circumscribed areas (CA) contain lymph. Note the trabeculae (T), the paratrabecular sinuses (PS) and the lymph nodule (N). H&E stain. X100.

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Figure 36: A photomicrograph of the mandibular lymph node from adult animal. Circumscribed areas (CA) in the medulla of the lobule surrounded by large amount of reticular fibres. Gomori’s silver stain. X100.

Figure 37: A photomicrograph of the mammary lymph node from adult animal. A subcapsular (SS) and paratrabecular sinuses (PS) are filled with blood. The corona (C) completely surrounds the germinal centre (GC) whereas the lymph nodule is located nearby two trabeculae. H&E stain. X40.

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Figure 38: A photomicrograph of the haemal node showing the capsule (C) and a large amount of blood inside circumscribed areas (CA) and inside diffuse lymphoid tissue (D). H&E stain. X40.

Figure 39: A photomicrograph of the haemal node. The circumscribed areas (CA) contain blood and connected with diffuse lymphoid tissue (arrows) that also contain blood. Masson’s trichrome stain. X 100.

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Figure 40: An electron micrograph of the mammary lymph node showing a capsule (C), and subcapsular sinuses lined with continuous endothelial cells (E), erythrocytes (Er) and lymphocytes (L). Lead citrate and uranyl acetate stain. X2000.

Figure 41: An electron micrograph of the parotid lymph node demonstrating part of a germinal centre with dividing cell (lymphoblast) (DC) in telophase. Lead citrate and uranyl acetate stain. X15000.

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Figure 42: An electron micrograph of the parotid lymph node. Small lymphocytes (SL) surrounded by distorted erythrocytes (E). The cytoplasm is in the form of a narrow rim surrounding a spherical nucleus with peripheral heterochromatin. Lead citrate and uranyl acetate stain. X12500.

Figure 43: An electron micrograph of the parotid lymph node. Medium-sized lymphocyte in germinal centre showing slightly irregular surface and provided with short microvilli (arrows). The oval nucleus (N) has heterochromatin mostly attaching to the nuclear membrane. Lead citrate and uranyl acetate stain. X15000.

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Table (1): Showing the average dimensions and weight of the parotid, mandibular, retropharyngeal, dorsal and ventral superficial cervical The node Wight (gm). Length/ cm. Width/ cm. Thic Min. Max. Aver. Min. Max. Aver. Min. Max. Aver. Min. Parotid 0.67 5.88 2.83 1.70 4.40 2.97 0.90 2.50 1.67 0.60 Mandibular 11.07 24.75 16.41 5.20 10.10 6.97 2.50 5.80 3.99 1.50 Retropharyngeal 3.74 12.70 7.52 4.60 6.90 5.50 2.20 4.20 3.04 0.90 D. S. C. 8.50 31.00 19.29 4.20 8.10 6.12 2.30 3.20 2.73 1.40 V. S. C. 12.80 48.10 30.72 4.60 8.00 6.35 4.10 6.20 4.66 1.60 lymph nodes.

D. S. C. =Dorsal Superficial Cervical. V. S. C. =Ventral Superficial Cervical.

221 Table 16: The volume fraction (Vv.) and the mean absolute volumes of components of the right and left mammary lymph nodes.

Sit C. T. G.C. C. D.L.T. B.&L.V. S. C.A. T.A e .V. of % cm % cm % cm % cm % cm % cm % cm the .³ .³ .³ .³ .³ .³ .³ no de Ri 16. 8.3 4.3 2.3 5.8 3.0 45. 23. 17. 9.1 9.0 4.5 0.7 0.3 51. ght 86 3 2 4 4 8 30 53 88 2 7 6 3 6 33 ±4. ±0. ±1. ±1. ±1. ±1. ±5. ±6. ±2. ±2. ±1. ±0. ±0. ±0. ±10 75 68 85 35 20 18 03 61 68 07 41 28 2 09 .26 Le 18. 8.9 3.6 1.9 4.9 2.5 44. 23. 19. 9.4 9.0 4.6 0.5 0.3 51. ft 18 4 5 4 2 8 62 50 02 2 3 2 8 3 33 ±5. ±2. ±1. ±1. ±1. ±1. ±5. ±9. ±3. ±2. ±1. ±1. ±0. ±0. ±17 08 72 38 08 10 18 54 81 27 10 28 70 31 25 .00

C. = Corona. S. = Sinuses. C.T. = Connective Tissue. G.C. = Germinal Centre. C.A. = Circumscribed Areas. B.&L.V. = Blood and Lymph Vessels. D.L.T. = Diffused Lymphatic Tissue. T.A.V. = Total Absolute Volume.

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Figure 44: An electron micrograph of the mammary lymph node. A granular leucocyte (eosinophil) showing kidney-shaped nucleus (N) and the cytoplasm is packed with large ovoid granules (G) that possess crystalloids. Lead citrate and uranyl acetate stain. X12.500.

Figure 45: An electron micrograph of the parotid lymph node. Part of a germinal centre showing a plasma cell filled with rough endoplasmic reticulum. The nucleus (N) is oval with peripheral heterochromatin. Lymphocytes (L) are also seen. Lead citrate and uranyl acetate stain. X10.000.

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