DIGESTION. 



237 



Structure. The oesophagus is made up of three coats viz., the outer, 

 mscular; the middle, submucous; and the inner, mucous. The mus- 

 cular coat (Fig. 175, g and i) is covered externally by a varying amount 

 >f loose fibrous tissue. It is composed of two layers of fibres, the outer 

 ?ing arranged longitudinally, and the inner circularly. At the upper 

 part of the oesophagus this coat is made up principally of striated muscle 

 fibres, as they are continuous with the constrictor muscles of the pharynx; 

 but lower down the unstriated fibres become more and more numerous, and 

 toward the end of the tube form the entire coat. The muscular coat is 

 connected with the mucous coat by a more or less developed layer of 



FIG. 173. Vertical section through a crypt of the human tonsil, a, entrance to the crypt, which 

 is divided below by the elevation which does not quite reach the surface ; 6, stratified epithelium ; c, 

 masses of adenoid tissue; d, mucous glands cut across; e, fibrous capsule. (V. D. Harris.) 



areolar tissue, which forms the submucous coat (Fig 175, /), in which is 

 contained in the lower half or third of the tube many mucous glands, the 

 ducts of which, passing through the mucous membrane (Fig. 175, c) open 

 on its surface. Separating this coat from the mucous membrane proper 

 is a well-developed layer of longitudinal, unstriated muscle (d), called 

 the muscular is mucosce. The mucous membrane is composed of a closely 

 felted meshwork of fine connective tissue, which, toward the surface, is 

 elevated into rudimentary papillae. It is covered with a stratified epithe- 

 lium, of which the most superficial layers are squamous. The epithelium 

 is arranged upon a basement membrane. 



In newly-born children the mucous membrane exhibits, in many parts, 

 the structure of lymphoid tissue (Klein). 



Blood and lymph vessels, and nerves, are distributed in the walls of 

 the oesophagus. Between the outer and inner layers of the muscular coat, 

 nerve-ganglia of Auerbach are also found. 



