THE FROG 



187 



passes by a duct into the gall bladder, gb, where it is stored 

 for a while and from which it later passes through the bile 

 duct into the duodenum, close to the pyloric end of the stomach. 

 In the bend of the U formed by the duodenum and the stomach, 

 is a slender, yellowish body, the pancreas, p, which empties into 

 the duodenum by the pancreatic duct opening close to the 

 bile duct. The lining of the whole alimentary canal is called 

 the mucous membrane. 



The whole intestine is slung in position by a thin sheet of 

 membrane, which passes around the intestine and then be- 

 comes attached to the abdominal wall. This is the mesentery, 

 and is really a fold of a large membrane that completely 

 lines the body cavity, the peritoneum. 

 The relations of the peritoneum, mes- 

 entery, and intestine are shown dia- 

 grammatically in Figure 91. In the 

 mesentery are many nerves and nu- 

 merous blood vessels which carry 

 nutrition from the intestine. The 

 mesentery surrounds not only the in- 

 testine, but also the liver and the 

 pancreas. In its folds below the 

 stomach is a rounded red body, the 

 spleen; Fig. 90 sp. 



Circulatory System. The circula- 

 tory system of the frog, like that of 

 the earthworm, consists of blood in- 

 closed in a network of blood vessels; but it is a more definite 

 system and the blood flows in a more regular course. It con- 

 sists of a true heart, and blood vessels. 



The heart is situated beneath the shoulder girdle, in front 

 of the liver and is surrounded by a thin sac, the pericardium 

 (Gr. peri = around + cardia = heart). The heart itself is 

 made up of a sac divided into three chambers, the walls of 

 which are masses of muscles. The fibers of these muscles run 



FIG. 91. DIAGRAM REP- 

 RESENTING A CROSS SEC- 

 TION OF THE BODY 



bw, body wall; 

 in, intestine; 

 mes, mesentery; 

 per, peritoneum. 



