392 STRUCTURE OF THE (ESOPHAGUS. [BOOK n. 



medullatecl fibres. As in the case of the salivary glands nerve-cells 

 are found in connection with the nerve-fibres as these pass into the 

 gland. 



The Structure of the (Esophagus. 



221. In the general plan of its structure the oesophagus 

 resembles the rest of the alimentary canal, for it consists of a 

 mucous membrane, with a muscularis mucosse and glands, a loose 

 submucous coat, and a muscular coat comprising an inner circular 

 and an outer longitudinal layer.V But the epithelium, epiblastic 

 in origin, is very different from that of the stomach or intestine, 

 and both circular and longitudinal muscular layers are composed 

 > to a large extent not of unstriated but of striated fibres like those 

 of the skeletal muscles. 



In a vertical section of the oesophagus it will be seen that the 

 epithelium is not arranged as a single layer of cells, but is several 

 cells deep. The lower cells near the basement membrane, which is 

 not very distinct, are cylindrical or spheroidal cells with granular 

 ' protoplasmic ' cell-substance, but those nearer the surface are 

 more flattened, and the uppermost cells are mere flattened nu- 

 cleated scales, the bodies of which are no longer protoplasmic 

 but have become changed into a peculiar material. Such an 

 epithelium is called a ' stratified ' epithelium. A similar epithe- 

 lium lines the greater part of the pharynx and the mouth, and 

 is continuous with the corresponding epithelium of the skin or 

 " epidermis " of which we shall have to speak later on. At the 

 cardiac orifice there is a sudden transition from this stratified 

 epithelium to the gastric epithelium previously described. 



The looseness of the submucous coat permits the mucous 

 membrane to be thrown into temporary longitudinal folds which 

 disappear when the canal is distended. But besides this, the line 

 of the basement membrane, of the connective tissue basis of 

 epithelium, ' dermis ' or ' corium ' as the corresponding part of the 

 skin is called, is raised up into a number of permanent conical 

 elevations or papillce, in which the connective tissue is especially 

 fine and which are richly provided with blood vessels. The surface 

 line of the epithelium does not follow the inequalities of the 

 dermis produced by these papilla^, but remains fairly even. In the 

 presence of these papillae the mucous membrane of the oesophagus 

 also resembles the skin, but in the latter structure the papillae are 

 more abundant and more regular in form and size. 



The dermis, or connective tissue basis of the epithelium, is a 

 network of fibres and fine bundles of connective tissue, with 

 connective tissue corpuscles and a considerable number of fine 

 elastic fibres ; the number of leucocytes in the meshes of the 

 network is relatively scanty. A few scattered masses of retiform 

 or adenoid tissue, of which we shall speak later on, occur here and 

 there. 



