DIGESTIVE SYSTEM 



747 



even in man it is closer to eleven inches in length than it is to twelve 

 inches in the adult. In the lower forms of animals it varies in length 

 and shape, as do all the other parts of the intestinal tract. 



Growing from this portion of the intestinal tract, immediately be- 

 yond the pylorus, in some of the ganoids and teleosts there may be as 

 many as one to two hundred blind tubes extending. These are known 

 as the pyloric caeca. There are a few elasmobranchs which have only 

 one pair of these caeca. These may be expanded into a pouch called 

 a bursa Entiana. The region of the intestine running caudad from the 

 duodenum is also called the post-hepatic intestine, and it is in this region 

 caudad to the liver, in which most of the digestive processes, as well as 

 most of the absorption of the products of digestion, take place. 



The food having been more or less mixed with various salivary 

 secretions, and having been reduced to a semi-liquid state, receives the 

 bile from the liver, and the pancreatic juice from the pancreas (Fig. 436). 



Fig. 436. 



A, The duodenum of a rabbit. P., Pyloric end of stomach ; yb., gall bladder 

 with bile duct and hepatic ducts ; p.d., pancreatic duct. (From Krause after 

 Claude Bernard.) 



B, Appendix vermiformis of kangaroo ; C, Appendix vermiformis of human 

 embryo. (After Wiedersheim. ) 



It is then ready, after being moved back and forth by the peristaltic 

 movement of the intestine, to be taken up and absorbed by the little 

 finger-like processes (villi) which extend from the inner surface of the 

 small intestine. As this has already been discussed it need not be en- 

 tered into again here. It is well, however, to remember that the length 

 of the intestine varies with the type of food the individual eats. It is 

 longer in plant-eating animals than in meat-eating animals. A classic 

 illustration of this is to compare the length of the intestine in the adult 

 frog with that of the tadpole. The adult frog's intestine is no longer 

 than that of a tadpole half the size a frog would be if it had kept up its 

 relative increase in size. 



Any blind pouch is called a caecum. At the beginning of the large 

 intestine where the small intestine enters into it, the joining itself is 

 called the ileo-caecal junction, and the little projecting end of the large 



