416 STRUCTURE OF THE (ESOPHAGUS. [BOOK n. 



form alveoli and they have no ducts. In the rabbit these cells are 

 rounded or polyhedral in form, and have a clear cell-substance with 

 a relatively large nucleus. Each of these groups is supplied with 

 blood vessels forming a capillary network more close set than else- 

 where. The exact nature of these cells is at present a matter of 

 doubt. 



The pancreas is supplied with nerves coming from the solar 

 plexus, and consisting partly of medullated and partly of non- 

 medullated 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. But the epithelium 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 

 1 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 papillae, but remains fairly even. In the 

 presence of these papillae the mucous membrane of the oesophagus 



