S Nov., 1907.] 



Elements of Animal Physiology. 



689 



PANCREAS. The duct of the liver has, in most animals (not in the solipeds 

 however), a pear-shaped dilatation called the gall bladder. The secretion 

 of the liver is called bile. The pancreas or sweetbread is, in part, 

 firmly attached to the duodenum ; its secretion is called -pancreatic juice. 



Tubular glands. 



Simple glands. Compound glands. 



Fig. 45. Simple and compound tubular glands. (After Stohr.) 



ADENOID TISSUE OF THE ALIMENTARY CANAL.— We have 

 seen in a former chapter that adenoid tissue is composed of densely packed 

 cells supported on a connective tissue frame-work. The alimentary canal is 

 fairly rich in this tissue. At the junction of the mouth and pharynx 

 are found two masses of adenoid tissue, one on either side, called the 

 TONSILS. In the mucous membrane of the pharynx many adenoid nodules 

 are found. In the oesophagus, crop and stomach adenoid tissue is present 

 in but small amounts. But in the small intestine we find large nodules 

 of it interrupting the mucous membrane and called Peyer's patches. 

 The caecum is also rich in this tissue which in some animals forms a definite 

 outgrowth called the vermiform appendix. Close to the stomach but 

 independent of the alimentary tul»e, is an organ composed wholly of 

 adenoid tissue and well supplied with blood vessels, called the spleen. 

 Of the functions of these adenoid organs we know nothing. 



MOVEMENTS OF THE ALIMENTARY CANAL.— Only in the 



mouth and pharynx, and in the oesophagus in varying degrees in different 

 animals, and around the anus do we find striped muscle which is under the 

 control of the will. In all other regions of the canal the muscle is smooth 

 and involuntary. The typical movement which the alimentary wall can 

 carry out is a worm-like motion by which the contents of the canal are 

 urged in the direction of the anus. The circular coat of muscle contracts 

 immediately headward of the food mass, and the constriction thus formed 

 is capable of passing like a wave for a short distance down the tube. 



