142 ELEMENTS OF MAMMALIAN ANATOMY 



The mucous coal of the small intestine contains tube-like 

 glands, the intestinal glands of Licberkiihn, whose secretion 

 acts on the sugars, assists the pancreatic juice in the digestion 

 of proteins, and contains a hormone which plays an important 

 role in the control of pancreatic secretion. In the duodenum 

 and jejunum the mucous membrane is thrown into numerous 

 transverse folds, valvuli conniventes, which increase the surface 

 for absorption. The villi are minute finger-like processes (Fig. 

 70), barely apparent to" the naked eye, projecting into the 

 lumen for the purpose of absorbing the nutriment from the 

 chyle. They consist of a covering of columnar epithelial cells 

 (Fig. 71a), within which ends a chyle vessel or lacteal surrounded 

 by small blood-vessels held in place by connective tissue. The 

 fatty portions of the food are carried by the lacteals (Fig. 716) to 

 the left thoracic duct, and thence to the jugular vein, while 

 other portions of the food are taken up by the capillaries of 

 the portal system, which begin in the villi (Fig. 71a). The 

 mucous membrane of the large intestine likewise contains tube- 

 like glands similar to the intestinal glands, but no villi. 



The submucous or areolar coat is adjacent to the mucous 

 coat of the intestine. It contains blood and lymphatic vessels, 

 nerve fibers and plexuses supplying the mucous coat. In cer- 

 tain regions of the digestive tube, as the duodenum and in 

 some mammals the esophagus, it also contains secreting glands 

 whole ducts penetrate the mucous coat and open upon the 

 epithelial surface. Next to the submucous coat is the muscular 

 coat, composed of tw^o layers, one of circular fibers, the other 

 of longitudinal fibers. An additional layer of oblique fibers 

 is present in the cardiac end of the stomach, which aid in 

 giving that organ the peculiar churning or peristaltic motion 

 necessary for chymification of the food. A fourth coat or 

 serous covering surrounds the muscular coat of the stomach 

 and intestines. It is merely a reflected portion of the perito- 

 neum which lines the entire abdominal cavity. 



