J. Anat. (1982), 135, 1, pp. 165-171 165 With 3 figures Printed in Great Britian The submucosal glands and the orientation of the musculature in the oesophagus of the camel M. N. JAMDAR AND A. N. E MA Department of Veterinary Anatomy, Faculty of Veterinary Medicine, Ahmadu Bello University, Zaria, Nigeria (Accepted 15 September 1981) INTRODUCTION The basic structure of the mammalian oesophagus is well known and was described many years ago by Goetsch (1910) among others. Such species variation as are known to occur involve especially the lining epithelium, the mucus secreting glands, the muscularis mucosae, and the extent of striated muscle in the wall. Studies have been reported on the oesophageal epithelium and its differentiation in the rat (Marques-Pereira & Leblond, 1965), on the developmental changes in the epithelium in man (John, 1952), on the fine structure of the epithelium in the newborn and adult mouse (Parakkal, 1967), and the synthesis of mucin by it in man (Mottet, 1970). The epithelium is always stratified squamous but may be keratinised in species whose diet is especially abrasive (e.g. in cattle, sheep, goat, horse: Delmann, 1971). The presence, number and distribution of the mucus secreting oesophageal glands in the submucosa are said to vary considerably in different species. Their presence is denied in the horse and cat by Bloom & Fawcett (1975) but claimed by Dellmann (1971), Dellmann & Brown (1976) and Trautman & Fiebeger (1949), at least in the pharyngo-oesophageal region of these species and of the ruminants (cattle, sheep, goat) in general. In man, the number of glands is extremely variable; they are few and scattered but are found throughout the oesophagus (Copenhaver, Bunge & Bunge, 1971; Di Fiore, 1977; Ham, 1974; Leeson & Leeson, 1970). The lamina muscularis mucosae is said to be present throughout the entire length of the oesophagus in the ruminants but is incomplete (Dellmann, 1971; Dellmann & Brown, 1976). The tunica muscularis externa usually consists of inner circular and outer long- itudinal muscle coats, the muscle being striated in the entire oesophagus in the ruminants and for the greater part of its length in the horse (Dellmann, 1971). Table 1 summarises the situation. Oesophageal innervation in the sheep (Dougherty, Habel & Bond, 1958) and the sphincteric action in eructation have been determined by Dougherty & Habel (1955). Wilkens & Rosenberger (1957) have studied the function of the oesophagus in relation to obstruction in swallowing in cattle. As will be seen from this brief review, little is known about the oesophagus of the camel (a ruminant) particularly about its glandular and muscular components, and a study of its histological features was thought to be of interest. 166 M. N. JAMDAR AND A. N. EMA Table 1. The arrangement of the structural components in the oesophagus ofsome of the domestic animals (after Dellmann, 1971) Lamina muscularis mucosae Tunica muscularis of smooth muscle (extent of striated Glands (location) (extent) muscle) Horse Pharyngo-oesophageal region Entire length of Down to last I oesophagus, in- to i complete Ruminants Pharyngo-oesophageal region Entire length of Entire length, oesophagus, in- to stomach complete Cat Pharyngo-oesophageal region Entire length of Down to last i oesophagus to I Man* Few and scattered, some Continuous and Upper i striated; being found throughout the thick middle third, oesophagus mixture of smooth and striated; lower i entirely smooth * From Copenhaver et al. (1971), Leeson & Leeson (1970) and Ham (1974). MATERIALS AND METHODS Tissue specimens of the oesophagus from various levels were collected from seven camels (euthanised and embalmed or freshly killed at the slaughter house) and preserved in 10 % formol saline. After processing by the standard histotechnique, the sections were cut at 6 ,um and stained with haematoxylin and eosin and Masson's trichrome stain. While pairing the tissue, care was taken to cut it exactly in the vertical plane to avoid artifact in orientation of the muscle fibres. The levels of the oesophagus from which the tissue was collected were as follows: (1) cranial-most part (pharyngeo-oesophageal junction); (2) mid-cervical; (3) mid-thoracic; (4) caudal- most part (near oesophago-ruminal junction). Detailed microscopic examination of the whole cross sections, as well as of longitudinal sections of the organ was made. Gross dissection was done to ascertain and confirm the direction of the muscle fibres in the tunica muscularis externa. RESULTS While the general structural characteristics were the same as in the oesophagus of other species of mammals, certain marked differences were seen from those reported so far for the ruminants. The differences were in respect of: (1) the type ofepithelium; (2) the level of the oesophagus at which the submucosal (oesophageal) glands occurred; (3) the presence of the lamina muscularis mucosae; (4) the orientation of the muscle fibres in the layers of the tunica muscularis externa. Epithelium There was heavy cornification of the epithelium. Glands and musculature of camel oesophagus 167 Fig. 1. Cross section of the entire oesophageal wall of the camel. The oesophageal glands (Gl) are densely distributed in the submucosa all round the wall. Lamina muscularis mucosa is absent. Outer muscle layer (Om) is circularly oriented; inner muscle layer (Im)S4ongitudinal. Mixed orientation in the muscle layers is also seen in places. The slide was projected on the screen and photographed. H & E. x 2-7. Oesophageal glands These were found throughout the length of the oesophagus. There were many, ovoid or elliptical, large and small clusters or lobules of tubulo-alveolar mucous glands in the submucosa, all round the wall of the oesophagus and more or less evenly spaced (Fig. 1). On average, 48 lobules were seen in a cross section. The alveolar cells in most alveoli were tall and of slender colummar shape. The glands appeared to be less numerous towards the caudal end of the oesophagus. Lamina muscularis mucosae This consisted of few, thin, scattered strands of smooth muscle, identifiable only in the caudal part of the oesophagus, being located deep the submucosal glands. In other words, the glands lay outside the muscularis mucosae where the latter was present. Elsewhere the lamina propria was continuous with r ie submucosa since the muscularis mucosae was deficient in most of the length ol the oesophagus. Tunica muscularis externa This was composed of striated (skeletal) muscle throughLout the length of the oesophagus. The peculiarity observed was in the arrangemenit of the tunicae. Although circularly arranged muscle fibres were present in the outer tunica there was also irregularity in the orientation of the muscle fibres in each one. This could be seen only by inspecting the entire cross sections of the specimens. In parts of the same section, the orientation was mixed. That is, in the outer tunica, the long- itudinally arranged fibres alternated with the circularly arranged ones, and vice versa in the inner tunica (Fig. 2). Obliquely oriented fibres occurred in some parts. In parts of both the cervical and caudal oesophagus, only longitudinal fibres in both the outer and inner tunica were seen. 168 M. N. JAMDAR AND A. N. EMA _% ' 8. Fig. 2. Photomicrograph of a cross section of the oesophagus of the camel in mid-thoracic region. Om, outer circular muscle layer; Im, inner longitudinal muscle layer; GI, oesophageal gland. H. & E. x 40. The circularly arranged muscle fibres in the outer tunica were more distinct in the mid-thoracic part of the oesophagus. Gross dissection and inspection confirmed these findings (Fig. 3). Nerve fibres in the tunica muscularis, as well as Auerbach's plexus, were seen. The latter was scanty and difficult to locate. Glands and musculature of camel oesophagus 169 OJln Fig. 3. Photograph of the dissected gross specimen of the camel oesophagus, mid-thoracic region. Adventitia is removed to show the outer circularly arranged muscle fibres. DISCUSSION Although species variations in certain structural components of the organs of the alimentary tract of domestic animals have been reported in the literature, sufficient detail is not available, particularly relating to the less studied species like the camel. The heavy cornification of the epithelium is obviously related to the coarse, dry food that the camel is required to consume. The other point in question is the general statement about the presence of submucosal (oesophageal) glands in the ruminants in the pharyngeo-oesophageal region only (Dellmann, 1971; Dellmann & Brown, 1976; Trautman & Fiebeger, 1949). The present investigation has revealed the presence of many oesophageal glands in the camel (allied to the ruminants) throughout the length of the oesophagus, a fact which has not been reported before. This apparent structural modification could be explained on the basis of the habitat of the camel and the foodstuffs available to it, there being need for more mucous glandular secretion for the passage of food of non-s-ucculent, or dry and rough type through its long oesophageal channel in a water-scarce environment. In man, the oesophageal glands are also found throughout the length of the oesophagus, but they are said to be few and scattered (Copenhaver et al. 1971). As for the ruminants like cattle, in which the glands are said to be confined only to the pharyngo-oesophageal region (Dellmann, 1971; Dellmann & Brown, 1976), green succulent food or pastures and water are generally available which, perhaps, obviate the necessity for mucous glands in the whole or the greater part of the oesophageal tract of these species. The same may be said of species like the horse and man. The presence of lamina muscularis mucosae in the form of a few scattered strands of smooth muscle, only in the caudal oesophagus of the camel, is also contrary to what is found in the ruminants. In the latter, the muscularis mucosae is reported to occur throughout the length of the oesophagus but to be incomplete (Dellmann, 170 M.