132 TOPOGRAPHICAL ANATOMY OF THE 



oesophagus, of which it may be regarded as au extension. Microscopic- 

 ally also it is like the oesophageal membrane, being without glands and 

 covered with stratified and squamous epithelium. At the cardia the 

 mucous membrane forms numerous folds that, with the abrupt and 

 oblique manner in which the oesophagus enters the stomach, must 

 render the return of food from the stomach to the oesophagus a matter 

 of some difficulty. The lining to the right of the margo plicatus is soft 

 and generally much folded. It can be divided into a darker portion to 

 the left, the fundus region, and a somewhat paler pyloric part. These 

 two regions differ in the structure of the glands contained within them. 

 It is generally possible also to distinguish a narrow yellowish or greyish 

 zone immediately adjoining the margo plicatus. This is the cardiac 

 gland zone. 



The mucous membrane should now be removed, the highly vascular 

 submucous tela noted, and the deepest layer of muscle exposed. The 

 deep muscular fibres are oblique in direction, and most plentiful about 

 the cardiac orifice, where they form an elongated loop, sometimes called 

 the sphincter cardia'. The oblique fibres, like the circular, are con- 

 tinuous with the circular fibres of the oesophagus. 



Interior of the duodenum. — The wall of the duodenum has the 

 same structure as that of the rest of the small intestine. The tube 

 should be slit open by an incision made along a line midway between 

 the two curvatures. 



At a distance of from 18 to 15 cm. from the pylorus, the mucous 

 membrane is considerably raised in the form of a tubular or saccular 

 diverticulum duodeni, opening into the duodenum by a conspicuous 

 orifice. If a probe be passed along the pancreatic and bile ducts 

 towards the duodenum, it can be demonstrated that these end in the 

 diverticulum, and that, consequently, the secretion they carry finds its 

 way into the duodenum by a common exit from the diverticulum. 



On the mucous membrane of the duodenal wall, opposite the diverti- 

 culum, is a much smaller papillary projection. On its summit is the 

 opening of the accessory pancreatic duct. 



Structure of the liver.— Some features of the structure of the 

 liver may be determined without microscopic examination. If the 

 surface of a slice of the gland be examined, the presence of polyhedral 

 areas of various size will be recognised. These are sections of the 

 hepatic lobules. In some aninials, the pig for example, the lobules are 

 clearly defined by a considerable quantity of interlobular connective 

 tissue. The healthy liver of the horse, however, contains only a small 



