METABOLISM IN VERTEBRATES 



• Esophagus 



Right atrium - 

 Pericardial cavity ■ 



\ Lung 



Left atrium 



Right ventricle 

 Diaphragm 



Stomach 

 Peritoneal cavity 



Small intestine 



Fig. 3.2. The coelomic cavities and coelomic viscera of man. 



taining a lung, and the peritoneal or abdominal cavity (Fig. 3.2). The peri- 

 cardial cavity lies between the two pleural cavities; these three cavities occupy 

 the chest or thoracic region of the trunk of the body. The peritoneal cavity 

 is located in the abdominal part of the trunk. It is here that the stomach, 

 small and large intestine, liver, and pancreas are found. 



Different degrees of folding and papillation occur in the stomach and small 

 intestine in the different groups of vertebrates, related to increase of the 

 surface of the lining epithelium. Various digestive glands are in the lining, 

 and it is the absorptive surface. In the small intestine, there is marked varia- 

 tion in the length which is correlated with the diet; the more concentrated 

 the diet, the shorter the small intestine. In the frog tadpole, which eats a 

 plant diet, the intestine is about 20 inches long, as compared with 12 inches 

 in the insect-feeding adult. Carnivorous mammals have shorter small intes- 

 tines than herbivorous ones, many of which have pouch-like outgrowths, or 

 caeca, correlated with retention of large quantities of low-calorie plant food. 

 The rudiment of such a caecum occurs in man near the junction of the small 

 and large intestine; it is known as the appendix. 



The liver and pancreas originate from the embryonic gut and remain at- 



49 



