THE DIGESTIVE SYSTEM 49 



which assist in the disintegration of the food. 

 The entrance to the cavity from the oesophagus 

 and the exit into the duodenum are close 

 together, and dorsal in position. 



A microscopic examination of the lining 

 membrane of the gizzard shows that much of 

 its thickness is due to the presence of the 

 dense horny lining (Fig. 21). Beneath this are 

 long, narrow, and simple glands, which reveal a 

 certain degree of grouping in their arrangement. 

 It is from these glands that the horny surface 

 layer of the mucous membrane is produced : 

 that is to say, the lining of the gizzard is 

 formed by hardened glandular secretion. 



Succeeding the stomach are the intestines, 

 generally measuring five or six times the 

 length of the body. Though the intestinal 

 tube varies little in width, it is customary to 

 distinguish small and large intestines. 



The small intestine, which begins at the 

 exit from the muscular stomach, is relatively 

 long and of uniform calibre throughout. Of 

 the three parts of the mammalian intestine — 

 duodenum, jejunum, and ileum — only the first 

 can be distinguished. There is no demarcation 

 between the jejunum and ileum, which are 

 disposed in coils and suspended from the 



