THE FROG 47 



treated in dealing with these. The whole of the alimentary canal 

 is lined by a thin cellular membrane, whose actual structure varies in 

 different parts, but as it is always kept moist by secretion from 

 some of its constituent cells, it is spoken of as the mucous membrane 

 or mucosa. 



The canal, its various parts, and the glands connected with 

 it, are kept in position by the same peritoneum that lines the coelomic 

 cavity, and this is reflected round them, so as to form thin sheets of 

 supporting tissue which bind them all together. The sheet that is 

 attached to the original dorsal side of the canal, and runs from it to 

 the body wall immediately beneath the vertebral column, is known 

 as a mesentery, while the various side folds tying different laterally 

 situated parts and organs to this main sheet are distinguished as 

 omenta. Thus the one enclosing the liver and joining it to the 

 stomach is known as the gastro-hepatic omentum. 



Intimately connected with the alimentary canal are two 

 important glands, the liver and the pancreas. The liver is a large 

 brownish mass situated just behind the heart, and occupying a large 

 part of the anterior end of the body cavity. It is composed of two 

 parts, one on each side of the middle line, the right and left lobes, 

 joined by a small connecting piece. The larger left lobe is partially 

 subdivided into two smaller lobes. Between the two main lobes is 

 situated a dark green spheroidal sac with thin walls, the gall-bladder, 

 in which the gall or bile secreted by the li ver is stored until required 

 for use. Three small ducts, the hepatic ducts, issue from the liver 

 substance and unite toform a common or cystic duct, that opens into 

 the bladder and serves for the conveyance of the bile fiom the liver. 

 Hence it is taken to the duodenum by a single tube, the bile duct or 

 ductus choledocus, which is formed by the union of three small tubes 

 coming from the cystic duct. This duct passes through the sub- 

 stance of the pancreas and some way along is joined by two or three 

 small ducts coming from the liver. Its point of entry into the 

 duodenum may easily be seen if the duodenum be slit up and washed 

 out, then when the gall bladder is pressed a drop of dark green liquid 

 will make its appearance on the wall of the intestine not far from the 

 pylorus. 



The pancreas is a pale yellow, slightly lobed, elongated 

 gland lying between the duodenum and the stomach, slightly towards 

 their dorsal side. It is traversed from end to end by the bile duct, 

 into which its own numerous small ducts open, so that it acts as a 

 common channel for bile and pancreatic fluid, and opens into 

 the duodenum shortly after leaving the posterior end of the 

 pancreas. 



Both the liver and pancreas, as we have seen, are connected 



