THE FROG 23 



with a lens and note outside the mucosa a thick muscular 

 layer; this in turn is covered externally by the very thin 

 glistening peritoneum. 



(3) The small intestine, into which the stomach is con- 

 tinued at its pyloric end. The first portion, which runs an- 

 teriorly, is the duodenum. Under cover of the liver the 

 duodenum bends posteriorly and the part of the small in- 

 testine posterior to the bend is known as the ileum. The 

 latter, after a number of coils, passes abruptly into : 



(4) The large intestine. The posterior part of the large 

 intestine is called the cloaca; this opens to the exterior by 

 the anus. 







If the animal has not been too long dead, observe the 

 peristaltic movements of the intestine (pinching the small 

 intestine with fine forceps will usually start these move- 

 ments). What is the function of these peristaltic move- 

 ments? The entire alimentary canal is fastened by a thin 

 membrane, the mesentery, to the dorsal body-wall. 



(b) The liver, already noticed, is a large dark-red organ 

 partly covering the duodenum and stomach. How many 

 lobes has it? On the dorsal side observe the gall bladder 

 or bile sac which is usually filled with green bile. Observe 

 the bile duct which extends from the gall bladder to the 

 duodenum, and the various hepatic ducts which enter the 

 bile duct from the liver. In a freshly-killed specimen, by 

 gently pressing the gall bladder and forcing bile from it into 

 the duct, the course of the bile duct may be more easily fol- 

 lowed. 



(c) The pancreas, a flat, irregularly-lobed yellowish 

 organ lying between the stomach and the duodenum and 

 stretching from the liver to the small intestine. The bile 



