THE VERTEBRATE BODY 



331 



staltic waves until it passes into the ileum which makes up the remainder 

 of the intestine. 



By this time the food moving through the intestine is chiefly in a 

 liquid state, for as food is digested it goes into solution. The protein- 

 splitting enzymes have broken the proteins down into amino acids, the 

 fat-splitting enzymes have changed the fats into fatty acids and glycerol, 

 and the starch-splitting enzymes have reduced the starch to sugar. 

 There are numerous longitudinal folds on the inside of the small in- 

 testine which increase the area exposed to the digesting food. These 

 folds are liberally supplied with capillaries. The liquid materials in the 



/ 



v. 



/ 



Oesophagus 



Cardium of stomach 



Liver 



Gall bladder 

 Pancreas 

 Bile duct 

 Duodenum 



Pyloric valve 

 Pylorus of stomach 

 Spleen 



Ileum 



Large intestine 



Urinary bladder 



Cloaca 

 Anus 



Fig. 23.1. The digestive system of a frog. The liver and pancreas have been folded 

 back from their normal position covering the duodenum and lower part of the stomach. 



