DOCSLIB.ORG

A Combined Approach of Teaching Head Development Using Embryology and Comparative Anatomy

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Combined Approach of Teaching Head Development Using Embryology and Comparative Anatomy Edorium J Anat Embryo 2016;3:17–27. Danowitz et al. 17 www.edoriumjournals.com/ej/ae REVIEW ARTICLE PEER REVIEWED | OPEN ACCESS A combined approach of teaching head development using embryology and comparative anatomy Melinda Danowitz, Hong Zheng, Adriana Guigova, Nikos Solounias ABSTRACT the evolutionary changes of many structures allows for a greater understanding of the Many aspects of human head embryology reflect human embryology, and removes the need for its evolutionary development. The pharyngeal memorization of seemingly complex processes. arches, a major component of head development, A link to comparative evolutionary anatomy originally functioned in filter feeding and provides context to the purpose and morphology vascular exchange, which is why each arch of primitive structures, and clarifies several has associated vasculature and muscles. The issues in human head development. primitive tongue had few-associated muscles and was responsible for simple movements; the Keywords: Anatomy education, Embryology, Head human tongue evolved post-otic somites that and neck, Pharyngeal arches migrate to the tongue and develop the majority of the tongue musculature. These somites originate How to cite this article outside the tongue, and the motor innervation therefore differs from the general and special Danowitz M, Zheng H, Guigova A, Solounias N. A sensory innervation. In the primitive condition, combined approach of teaching head development the trapezius and sternocleidomastoid belonged using embryology and comparative anatomy. to a single muscle group that were involved in Edorium J Anat Embryo 2016;3:17–27. gill movements; they separate into two muscles with the reduction of certain skeletal elements, but retain the same innervation. Examining Article ID: 100011A04MD2016 ********* Melinda Danowitz1, Hong Zheng2, Adriana Guigova3, Nikos doi:10.5348/A04-2016-11-RA-3 Solounias4 Affiliations: 1BA, Medical Student, Anatomy, New York In- stitute of Technology College of Osteopathic Medicine, Old Westbury, NY, USA; 2DO, Resident, Vascular Surgery, Phila- INTRODUCTION delphia College of Osteopathic Medicine, Philadelphia, PA, USA; 3DO, Fellow, Hematology/oncology, North Shore- Long The development of the human head is of critical Island Jewish, New Hyde Park, NY, USA; 4PhD, Professor, Anatomy, New York Institute of Technology College of Os- importance to the medical students, as a complete teopathic Medicine, Old Westbury, NY, USA. understanding is necessary to comprehend pathologies Corresponding Author: Nikos Solounias, 8000 Northern such as cleft lip and palate, Treacher Collins syndrome, Boulevard, Old Westbury, NY, USA, 11568; Email: nsol- and DiGeorge syndrome, among many others. These [email protected] pathologies have been studied in mice in addition to humans, allowing for the establishment of genetic homologies [1–3]. The embryology of the human head is Received: 06 February 2016 strongly related to the evolutionary history of vertebrate Accepted: 04 March 2016 head and neck. We believe a link to comparative Published: 16 April 2016 evolutionary anatomy is needed, as it provides context to Edorium Journal of Anatomy and Embryology, Vol. 3; 2016. Edorium J Anat Embryo 2016;3:17–27. Danowitz et al. 18 www.edoriumjournals.com/ej/ae the original purpose and development of early structures. combined tissues from all three germ layers. The sections An AAMC 2000 Graduation Survey revealed that 73% of this study are the components of the head. Each is of respondents never took a premedical comparative treated here separately but they all interact and form an anatomy course [4]. The American Association of integrated whole. Many of the interactions take place Medical Colleges and the Howard Hughes Medical simultaneously. Institute recommended that evolutionary biology should be included in medical education [5]. Without BRAIN, HEART, PHARYNX, AND an understanding of the evolutionary history, head NOTOCHORD embryology can be an overly complex topic that involves The head begins to form with interactions between a great deal of memorization. Furthermore, anomalous four basic early structures: brain, heart, pharynx and anatomical presentations often reflect the typical notochord (Figure 1). The brain forms as an involuting morphology in more primitive animals; studies of human set of neural folds from the rostral end of the neural biliary tract and limb musculature variations revealed tube. The original embryological external surface of the that the atypical human structures resembled the normal neural tube will ultimately form the internal folds and condition seen in other animals [6, 7]. ventricles of the brain. The early heart develops anterior The study of evolutionary biology relates not only to to the brain. As development progresses, the heart slowly anatomy and embryology, but also to medicine in general. swings posteriorly and many of its arteries will become At the molecular level, evolution helps biologists study incorporated into the pharynx as the pharyngeal arch genetic mutations that allow viruses to infect multiple arteries (Figure 1). Thus, the proximal heart circulation is species, or how pathogens gain virulence [8]. Darwinian medicine also facilitates comprehension about natural selection, and which aspects of the human body are vulnerable to, or protected against disease [5]. Natural selection explains malarial resistance in sickle-cell trait carriers, and can potentially clarify associations between breast cancer and birth control [9]. Studies of medical education curricula in the UK as well as in North America demonstrated an overall need for the incorporation of evolutionary biology into medical courses [10, 11]. The evolutionary origin of the skull, face, and neck has been extensively studied from a scientific standpoint [12– 15]. For example, studies involving transplanting avian embryonic cells and tracking the differentiation of cranial tissues gave insight into the fate of mesodermal and neural crest cells [16]. We aim to link human head embryology with evolutionary history at a level understandable for medical students. We, therefore, provide a brief description of the evolutionary history of each process involved in head development, to provide context to the embryonic structures and ultimate derivatives, and to help students understand why the human anatomy develops from the early embryo the way it does. We currently provide a comprehensive summary of Figure 1: Internal and external view of the developing head the development of the human head. The aim for this and neck at week 4. (A) Ventral view depicting the early heart, article is to be used as a supplement to the various medical maxillary and mandibular processes of arch 1, arch 2, and the oropharyngeal membrane with several perforations. (B) Cross embryology textbooks. We believe the abbreviated yet sectional view showing the relationship between the folding comprehensive summary of head and neck embryology, neural groove, pharyngeal arch contents, and notochord. The supplemented with a section describing the comparative otic placode is depicted before penetrating the head to form the evolutionary anatomy, will enable medical students to otic vesicle. The pharyngeal arch contains an associated artery, better understand the development of the head. vein, nerve, muscle, and cartilage, all of which are capped by an intramembranous ossification. The dorsal aorta is initially a THE GENERAL DEVELOPMENT OF THE bilateral structure with the notochord positioned at the midline; the aortae fuse to form a single vessel during week 4. (C) Lateral HUMAN HEAD view representing the developing heart, head, and neck. Arch 1 The head is formed by the interaction of the three has a dorsal and ventral component, separated by the temporal- basic tissues: ectoderm, mesoderm and endoderm. When mandibular hinge joint (TMJ). (D) Internal view emphasizing the head is fully differentiated, its parts are the result of the interrelationship between the pharyngeal arches and arterial branches, as well as the notochord and developing brain. Edorium Journal of Anatomy and Embryology, Vol. 3; 2016. Edorium J Anat Embryo 2016;3:17–27. Danowitz et al. 19 www.edoriumjournals.com/ej/ae closely related to the head. Pharyngeal, or branchial arches processes (maxillary and mandibular processes) whose are 6 units of complex tissues aligned in a sequence. The derivatives are ultimately connected by a hinge joint pharynx has pouches and clefts along its length. A cleft- (temporomandibular joint) (Figure 1). The upper jaw pouch unit alternates with an arch. The clefts (externally) (maxilla) is not derived from the first arch pharyngeal and the pouches (internally) correspond to each other cartilages. The pharynx is an internal space around which and are separated by a membrane (Figure 2). Cleft 1 is the arches appear to wrap around. The arches and the the only cleft that persists in humans; the first cleft and cleft-pouch units constitute the wall of the pharynx. The pouch fuse to form the tympanic membrane of the ear. median area is the pharyngeal floor, which constitutes All other clefts are obliterated by the down growth of the mucosal surface, but not the internal muscles, of the the platysma muscle from arch 2. Each pharyngeal arch tongue [17]. includes an associated artery, vein, a branchiomeric The anterior part of the pharynx connects to an cranial nerve, muscles, cartilage, and neural crest cells. external tunnel, the stomodeum, which forms under the Pharyngeal arch 1 is the
Load more

Recommended publications
  • Te2, Part Iii
    TERMINOLOGIA EMBRYOLOGICA Second Edition International Embryological Terminology FIPAT The Federative International Programme for Anatomical Terminology A programme of the International Federation of Associations of Anatomists (IFAA) TE2, PART III Contents Caput V: Organogenesis Chapter 5: Organogenesis (continued) Systema respiratorium Respiratory system Systema urinarium Urinary system Systemata genitalia Genital systems Coeloma Coelom Glandulae endocrinae Endocrine glands Systema cardiovasculare Cardiovascular system Systema lymphoideum Lymphoid system Bibliographic Reference Citation: FIPAT. Terminologia Embryologica. 2nd ed. FIPAT.library.dal.ca. Federative International Programme for Anatomical Terminology, February 2017 Published pending approval by the General Assembly at the next Congress of IFAA (2019) Creative Commons License: The publication of Terminologia Embryologica is under a Creative Commons Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0) license The individual terms in this terminology are within the public domain. Statements about terms being part of this international standard terminology should use the above bibliographic reference to cite this terminology. The unaltered PDF files of this terminology may be freely copied and distributed by users. IFAA member societies are authorized to publish translations of this terminology. Authors of other works that might be considered derivative should write to the Chair of FIPAT for permission to publish a derivative work. Caput V: ORGANOGENESIS Chapter 5: ORGANOGENESIS
    [Show full text]
  • Induction and Specification of Cranial Placodes ⁎ Gerhard Schlosser
    Developmental Biology 294 (2006) 303–351 www.elsevier.com/locate/ydbio Review Induction and specification of cranial placodes ⁎ Gerhard Schlosser Brain Research Institute, AG Roth, University of Bremen, FB2, PO Box 330440, 28334 Bremen, Germany Received for publication 6 October 2005; revised 22 December 2005; accepted 23 December 2005 Available online 3 May 2006 Abstract Cranial placodes are specialized regions of the ectoderm, which give rise to various sensory ganglia and contribute to the pituitary gland and sensory organs of the vertebrate head. They include the adenohypophyseal, olfactory, lens, trigeminal, and profundal placodes, a series of epibranchial placodes, an otic placode, and a series of lateral line placodes. After a long period of neglect, recent years have seen a resurgence of interest in placode induction and specification. There is increasing evidence that all placodes despite their different developmental fates originate from a common panplacodal primordium around the neural plate. This common primordium is defined by the expression of transcription factors of the Six1/2, Six4/5, and Eya families, which later continue to be expressed in all placodes and appear to promote generic placodal properties such as proliferation, the capacity for morphogenetic movements, and neuronal differentiation. A large number of other transcription factors are expressed in subdomains of the panplacodal primordium and appear to contribute to the specification of particular subsets of placodes. This review first provides a brief overview of different cranial placodes and then synthesizes evidence for the common origin of all placodes from a panplacodal primordium. The role of various transcription factors for the development of the different placodes is addressed next, and it is discussed how individual placodes may be specified and compartmentalized within the panplacodal primordium.
    [Show full text]
  • Vocabulario De Morfoloxía, Anatomía E Citoloxía Veterinaria
    Vocabulario de Morfoloxía, anatomía e citoloxía veterinaria (galego-español-inglés) Servizo de Normalización Lingüística Universidade de Santiago de Compostela COLECCIÓN VOCABULARIOS TEMÁTICOS N.º 4 SERVIZO DE NORMALIZACIÓN LINGÜÍSTICA Vocabulario de Morfoloxía, anatomía e citoloxía veterinaria (galego-español-inglés) 2008 UNIVERSIDADE DE SANTIAGO DE COMPOSTELA VOCABULARIO de morfoloxía, anatomía e citoloxía veterinaria : (galego-español- inglés) / coordinador Xusto A. Rodríguez Río, Servizo de Normalización Lingüística ; autores Matilde Lombardero Fernández ... [et al.]. – Santiago de Compostela : Universidade de Santiago de Compostela, Servizo de Publicacións e Intercambio Científico, 2008. – 369 p. ; 21 cm. – (Vocabularios temáticos ; 4). - D.L. C 2458-2008. – ISBN 978-84-9887-018-3 1.Medicina �������������������������������������������������������������������������veterinaria-Diccionarios�������������������������������������������������. 2.Galego (Lingua)-Glosarios, vocabularios, etc. políglotas. I.Lombardero Fernández, Matilde. II.Rodríguez Rio, Xusto A. coord. III. Universidade de Santiago de Compostela. Servizo de Normalización Lingüística, coord. IV.Universidade de Santiago de Compostela. Servizo de Publicacións e Intercambio Científico, ed. V.Serie. 591.4(038)=699=60=20 Coordinador Xusto A. Rodríguez Río (Área de Terminoloxía. Servizo de Normalización Lingüística. Universidade de Santiago de Compostela) Autoras/res Matilde Lombardero Fernández (doutora en Veterinaria e profesora do Departamento de Anatomía e Produción Animal.
    [Show full text]
  • Loss-Of-Function Mutation in the Prokineticin 2 Gene Causes
    Loss-of-function mutation in the prokineticin 2 gene SEE COMMENTARY causes Kallmann syndrome and normosmic idiopathic hypogonadotropic hypogonadism Nelly Pitteloud*†, Chengkang Zhang‡, Duarte Pignatelli§, Jia-Da Li‡, Taneli Raivio*, Lindsay W. Cole*, Lacey Plummer*, Elka E. Jacobson-Dickman*, Pamela L. Mellon¶, Qun-Yong Zhou‡, and William F. Crowley, Jr.* *Reproductive Endocrine Unit, Department of Medicine and Harvard Reproductive Endocrine Science Centers, Massachusetts General Hospital, Boston, MA 02114; ‡Department of Pharmacology, University of California, Irvine, CA 92697; §Department of Endocrinology, Laboratory of Cellular and Molecular Biology, Institute of Molecular Pathology and Immunology, University of Porto, San Joa˜o Hospital, 4200-465 Porto, Portugal; and ¶Departments of Reproductive Medicine and Neurosciences, University of California at San Diego, La Jolla, CA 92093 Communicated by Patricia K. Donahoe, Massachusetts General Hospital, Boston, MA, August 14, 2007 (received for review May 8, 2007) Gonadotropin-releasing hormone (GnRH) deficiency in the human associated with KS, although no functional data on the mutant presents either as normosmic idiopathic hypogonadotropic hypo- proteins were provided (17). Herein, we demonstrate that homozy- gonadism (nIHH) or with anosmia [Kallmann syndrome (KS)]. To gous loss-of-function mutations in the PROK2 gene cause IHH in date, several loci have been identified to cause these disorders, but mice and humans. only 30% of cases exhibit mutations in known genes. Recently, murine studies have demonstrated a critical role of the prokineticin Results pathway in olfactory bulb morphogenesis and GnRH secretion. Molecular Analysis of PROK2 Gene. A homozygous single base pair Therefore, we hypothesize that mutations in prokineticin 2 deletion in exon 2 of the PROK2 gene (c.[163delA]ϩ [163delA]) (PROK2) underlie some cases of KS in humans and that animals was identified in the proband, in his brother with KS, and in his deficient in Prok2 would be hypogonadotropic.
    [Show full text]
  • Anatomical Basis of Craniofacial Birth Defects
    AnatomicalAnatomical BasisBasis ofof CraniofacialCraniofacial BirthBirth DefectsDefects Handout download: http://www.oucom.ohiou.edu/dbms-witmer/peds-rpac.htm LawrenceLawrence M.M. Witmer,Witmer, PhDPhD Department of Biomedical Sciences College of Osteopathic Medicine Ohio University Athens, Ohio 45701 [email protected] 18 October 2000 DevelopmentDevelopment ofof thethe FaceFace II • 5 facial primordia • Frontonasal prominence • Paired maxillary prominences • Paired mandibular prominences • Surround primordial mouth (stomodeum) • Neural crest: source for almost all connective tissues in the face • Frontonasal prominence forms forehead and nose and a short margin of mouth • Lower jaw and lip form first • Nasal placodes (and pit): surrounded by medial & lateral nasal prominences • Nasal pit remains connected to mouth • Maxillary prominences grow toward each other, pushing nasal prominences medially From Moore 1982 DevelopmentDevelopment ofof thethe FaceFace IIII • Medial nasal prominences merge with each other and with lateral nasal & maxillary prominences • Nasolacrimal groove: between lateral nasal and maxillary prominences • Becomes nasolacrimal duct • Duct forms as solid epithelial cord that later canalizes • Nasolacrimal duct atresia • Failure to completely canalize • 6% of newborns • Intermaxillary segment • Merger of medial nasal prominences • Gives rise to philtrum, premaxillary bones, primary palate From Moore 1982 SummarySummary ofof FacialFacial DevelopmentDevelopment From Moore 1982 Disruptions in the formation
    [Show full text]
  • Development and Malformations of Face and Palate
    Development and malformations of face and palate Compiled by András Csillag and Andrea D. Székely GERMINAL LAYER DERIVATIVES ECTODERM contributing to the formation of the face appears by the 4th week. The oropharyngeal membrane (interface between ECTODERM and ENDODERM) is located in front of the later palatine tonsils. Ectodermal structures limiting the stomodeum participate in the formation of the face, as well as of the nasal and oral cavities. MESENCHYME that fills the pharyngeal arches derives from the neural crest ECTOMESENCHYME DEVELOPMENT OF THE FACE WEEK 6 The face is formed by 5 processes approximately 24 days Frontonasal prominence (1) Maxillary prominence (2) 1st arch Mandibular prominence (2) nasal (olfactory) pits form surrounded by the medial and lateral nasal processes nasolacrimal groove separates the lateral nasal process from the maxillary process maxillary processes fuse with the medial nasal processes lateral nasal processes fuse with the maxillary processes, thus obliterating the nasolacrimal groove. DEVELOPMENT OF THE FACE 5-week embryo 6-week embryo 7-week embryo. 10-week embryo The nasal prominences are gradually Maxillary prominences have fused separated from the maxillary with the medial nasal prominences. prominence by deep furrows. CEPHALIC PRIMORDIA - PLACODES Olfactory placode Pharyngeal Stomodeum” arches Nasal placodes - thickenings of the surface ectoderm (later differentiate into the olfactory epithelium) DEVELOPMENT OF THE NASAL CAVITIES AND THE HARD PALATE By week 5 the placodes form the nasal pits. They further invaginate and the pits approach the primitive oral cavity. A thin oronasal membrane separates the two cavities. By its rupture the primitive choanae will form DEVELOPMENT OF THE NASAL CAVITIES AND THE HARD PALATE By week 8, a partition forms between the primitive nasal chambers and the oral cavity The primary palate - the anterior aspect derives from the intermaxillary segment (or median palatine process, formed by the medial nasal processes).
    [Show full text]
  • Syndromes of the First and Second Branchial Arches, Part 1: Embryology and Characteristic REVIEW ARTICLE Defects
    Syndromes of the First and Second Branchial Arches, Part 1: Embryology and Characteristic REVIEW ARTICLE Defects J.M. Johnson SUMMARY: A variety of congenital syndromes affecting the face occur due to defects involving the G. Moonis first and second BAs. Radiographic evaluation of craniofacial deformities is necessary to define aberrant anatomy, plan surgical procedures, and evaluate the effects of craniofacial growth and G.E. Green surgical reconstructions. High-resolution CT has proved vital in determining the nature and extent of R. Carmody these syndromes. The radiologic evaluation of syndromes of the first and second BAs should begin H.N. Burbank first by studying a series of isolated defects: CL with or without CP, micrognathia, and EAC atresia, which compose the major features of these syndromes and allow more specific diagnosis. After discussion of these defects and the associated embryology, we proceed to discuss the VCFS, PRS, ACS, TCS, Stickler syndrome, and HFM. ABBREVIATIONS: ACS ϭ auriculocondylar syndrome; BA ϭ branchial arch; CL ϭ cleft lip; CL/P ϭ cleft lip/palate; CP ϭ cleft palate; EAC ϭ external auditory canal; HFM ϭ hemifacial microsomia; MDCT ϭ multidetector CT; PRS ϭ Pierre Robin sequence; TCS ϭ Treacher Collins syndrome; VCFS ϭ velocardiofacial syndrome adiographic evaluation of craniofacial deformities is nec- major features of the syndromes of the first and second BAs. Ressary to define aberrant anatomy, plan surgical proce- Part 2 of this review discusses the syndromes and their radio- dures, and evaluate the effects of craniofacial growth and sur- graphic features: PRS, HFM, ACS, TCS, Stickler syndrome, gical reconstructions.1 The recent rapid proliferation of and VCFS.
    [Show full text]
  • Characterization of Epithelial Domains in The
    Development 106, 493-509 (1989) 493 Printed in Great Britain © The Company of Biologists Limited 1989 Characterization of epithelial domains in the nasal passages of chick embryos: spatial and temporal mapping of a range of extracellular matrix and cell surface molecules during development of the nasal placode S. J. CROUCHER and C. TICKLE Department of Anatomy and Developmental Biology, University College & Middlesex School of Medicine, Windeyer Building, Cleveland Street, London W1P6DB, UK Summary The formation of the nasal passages involves complex development to gain insights into the origin of the morphogenesis and their lining develops a spatially epithelial lining of the nasal passages. All reagents bind ordered pattern of differentiation, with distinct domains at early stages to the thickened nasal placode and of olfactory and respiratory epithelium. Using anti- surrounding head ectoderm and then become progress- bodies to the neural cell adhesion molecule (N-CAM), ively restricted to the olfactory domain. The expression keratan sulphate and heparan sulphate proteoglycan of these characteristics appears to be modulated during (HSPG) and a panel of lectins (agglutinins of Canavalia development rather than being cell autonomous. ensiformis (ConA), Dolichos biflorus (DBA), peanut The distribution of keratan sulphate was compared (PNA), Ricinis communis (RCA1), soybean (SBA), Ulex with collagen type II in relation to the specification of the europaeus (UEA1), and wheatgerm (WGA)), we have chondrocranium. Keratan sulphate and collagen type II documented cell surface characteristics of each epithelial are only colocalized at the epithelial-mesenchymal inter- domain. Binding of antibodies to N-CAM and to keratan face during early nasal development. At later stages, sulphate, and the lectins ConA, PNA, RCA1, SBA and only collagen type II is expressed at the interface WGA marks the olfactory epithelial domain only.
    [Show full text]
  • Congenital Anomalies of the Nose
    133 Congenital Anomalies of the Nose Jamie L. Funamura, MD1 Travis T. Tollefson, MD, MPH, FACS2 1 Department of Otolaryngology and Communication Enhancement, Address for correspondence Travis T. Tollefson, MD, MPH, FACS, Facial Children’s Hospital Boston, Boston, Massachusetts Plastic and Reconstructive Surgery, Department of Otolaryngology- 2 Department of Otolaryngology, University of California, Davis, Head and Neck Surgery, University of California, Davis, 2521 Stockton Sacramento, California Blvd., Suite 7200, Sacramento, CA 95817 (e-mail: [email protected]). Facial Plast Surg 2016;32:133–141. Abstract Congenital anomalies of the nose range from complete aplasia of the nose to duplications and nasal masses. Nasal development is the result of a complex embryo- logic patterning and fusion of multiple primordial structures. Loss of signaling proteins or failure of migration or proliferation can result in structural anomalies with significant Keywords cosmetic and functional consequences. Congenital anomalies of the nose can be ► nasal deformities categorized into four broad categories: (1) aplastic or hypoplastic, (2) hyperplastic or ► nasal dermoid duplications, (3) clefts, and (4) nasal masses. Our knowledge of the embryologic origin ► Tessier cleft of these anomalies helps dictate subsequent work-up for associated conditions, and the ► nasal cleft appropriate treatment or surgical approach to manage newborns and children with ► nasal hemangioma these anomalies. – Congenital anomalies of the nose are thought to be relatively side1 4 (►Fig. 1A, B). The medial processes will ultimately fuse, rare, affecting approximately 1 in every 20,000 to 40,000 live contributing to the nasal septum and the medial crura of the births.1 The exact incidence is difficult to quantify, as minor lower lateral cartilages.
    [Show full text]
  • EMBRYOLOGY7 Dr.Ban A.Ghani Developmdent of External
    EMBRYOLOGY7 Dr.Ban A.Ghani EMBRYOLOGY7 Dr.Ban A.Ghani Developmdent of external /Sequence of developmental During the third week of development an oropharyngeal membrane buccopharyngeal , or oral membrane) is first seen at the site of the future face, between the primordium of the heart and the rapidly enlarging primordium of the brain. It is composed of ectoderm externally and endoderm internally. It lies at the beginning of the digestive tract and breaks down during the 4th week in order to form the opening between the future oral cavity (primitive mouth or stomodeum) and the foregut. The oropharyngeal membrane breaks down when it stops growing. While tissues around it expand very rapidly, the oropharyngeal membrane’s non-proliferating cells are gradually pulled apart because they cannot fill the expanding area. The human face begins to form during the 4th week of embryonic development. By the 6th week the external face is completed. The development of the palate subdivides nasal and oral cavities. This development continues into the 12th week with completion of the soft palate. Human face during the 4th prenatal week. Around the centrally located oral pit are grouped the frontal and maxillary processes and the mandibular arch. 1 EMBRYOLOGY7 Dr.Ban A.Ghani Human face during the 5th prenatal week. The nasal pits develop and appear on the sides of the face. The frontal process now becomes the frontonasal process Human face during the 6th prenatal week. Nasal pits appear more centrally located in the medial nasal process. This is the result of growth of the lateral face, which also causes the eyes to approach the front of the face.
    [Show full text]
  • Evolution of the Nasal Structure in the Lower Tetrapods
    AM. ZOOLOCIST, 7:397-413 (1967). Evolution of the Nasal Structure in the Lower Tetrapods THOMAS S. PARSONS Department of Zoology, University of Toronto, Toronto, Ontario, Canada SYNOPSIS. The gross structure of the nasal cavities and the distribution of the various types of epithelium lining them are described briefly; each living order of amphibians and reptiles possesses a characteristic and distinctive pattern. In most groups there are two sensory areas, one lined by olfactory epithelium with nerve libers leading to the main olfactory bulb and the other by vomeronasal epithelium Downloaded from https://academic.oup.com/icb/article/7/3/397/244929 by guest on 04 October 2021 with fibers to the accessory bulb. All amniotes except turtles have the vomeronasal epithelium in a ventromedial outpocketing of the nose, the Jacobson's organ, and have one or more conchae projecting into the nasal cavity from the lateral wall. Although urodeles and turtles possess the simplest nasal structure, it is not possible to show that they are primitive or to define a basic pattern for either amphibians or reptiles; all the living orders are specialized and the nasal anatomy of extinct orders is unknown. Thus it is impossible, at present, to give a convincing picture of the course of nasal evolution in the lower tetrapods. Despite the rather optimistic title of this (1948, squamates), Stebbins (1948, squa- paper, I shall, unfortunately, be able to do mates), Bellairs and Boyd (1950, squa- iittle more than make a few guesses about mates), and Parsons (1959a, reptiles). Most the evolution of the nose. I can and will of the following descriptions are based on mention briefly the major features of the these works, although others, specifically nasal anatomy of the living orders of cited in various places, were also used.
    [Show full text]
  • A New Origin for the Maxillary Jaw
    Developmental Biology 276 (2004) 207–224 www.elsevier.com/locate/ydbio A new origin for the maxillary jaw Sang-Hwy Leea, Olivier Be´dardb,1, Marcela Buchtova´b, Katherine Fub, Joy M. Richmanb,* aDepartment of Oral, Maxillofacial Surgery and Oral Science Research Center, Medical Science and Engineering Research Center, BK 21 Project for Medical Science, College of Dentistry Yonsei University, Seoul, Korea bDepartment of Oral Health Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada, V6T 1Z3 Received for publication 7 April 2004, revised 5 August 2004, accepted 31 August 2004 Available online 5 October 2004 Abstract One conserved feature of craniofacial development is that the first pharyngeal arch has two components, the maxillary and mandibular, which then form the upper and lower jaws, respectively. However, until now, there have been no tests of whether the maxillary cells originate entirely within the first pharyngeal arch or whether they originate in a separate condensation, cranial to the first arch. We therefore constructed a fate map of the pharyngeal arches and environs with a series of dye injections into stage 13–17 chicken embryos. We found that from the earliest stage examined, the major contribution to the maxillary bud is from post-optic mesenchyme with a relatively minor contribution from the maxillo-mandibular cleft. Cells labeled within the first pharyngeal arch contributed exclusively to the mandibular prominence. Gene expression data showed that there were different molecular codes for the cranial and caudal maxillary prominence. Two of the genes examined, Rarb (retinoic acid receptor b) and Bmp4 (bone morphogenetic protein) were expressed in the post-optic mesenchyme and epithelium prior to formation of the maxillary prominence and then were restricted to the cranial half of the maxillary prominence.
    [Show full text]