884 ANATOMY AND DEVELOPMENT 



The connective tissue and muscular coats are extremely 

 thin. There is present everywhere a peritoneal covering, and 

 in front a fairly well-marked though very thin layer of muscles 

 formed of an external circular and an internal longitudinal 

 layer. In the middle and posterior parts, however, I was un- 

 able to recognize these two layers in section ; although in surface 

 view Grube found an inner layer of circular fibres and an outer 

 layer formed of bands of longitudinal fibres, which he regards as 

 muscular. 



The layer supporting the epithelium is reduced to a base- 

 ment membrane. The epithelial part of the wall of the stomach 

 is by far the thickest (fig. 20), and is mainly composed of enor- 

 mously elongated, fibre-like cells, which in the middle part of 

 the stomach, where they are longest, are nearly half a millimetre 

 in length, and only about "006 mm. in breadth. Their nuclei, as 

 seen in fig. 20, are very elongated, and are placed about a quar- 

 ter of the length from the base. 



The cells are mainly filled with an immense number of 

 highly refracting spherules, probably secretory globules, but 

 held by Grube, from the fact of their dissolving in ether, to be 

 fat. The epithelial cells are raised into numerous blunt pro- 

 cesses projecting into the lumen of the stomach. 



In addition to the cells just described there are present in 

 the anterior part of the stomach a fair sprinkling of mucous 

 cells. There are also everywhere present around the bases of 

 the columnar cells short cells with spherical nuclei, which are 

 somewhat irregularly scattered in the middle and posterior parts 

 of the stomach, but form in the front part a definite layer. I 

 have not been able to isolate these cells, and can give no ac- 

 count of their function. 



The rectum extends from the end of the stomach to the 

 anus. The region of junction between the stomach and the 

 rectum is somewhat folded. The usual arrangement of the 

 parts is shewn in fig. 6, where the hind end of the stomach is 

 seen to be bent upon itself in a U-shaped fashion, and the 

 rectum extending forwards under this bent portion and joining 

 the front end of the dorsal limb of the U. The structure of 

 the walls of the rectum is entirely different to that of the 

 stomach, and the transition between the two is perfectly sudden. 



