THE DOGFISH 11 



through the walls of which the outlines of the spiral valve may 

 be seen. Behind the large intestine is a short tube, the colon, 

 which, in turn, passes into the rectum, the line between colon 

 and rectum being marked on the dorsal side by a finger-shaped 

 rectal gland. The hinder part of the digestive tract will be 

 studied later. At the junction of pylorus and duodenum is the 

 lobate pancreas; how many lobes and how arranged? 



Sketch the viscera thus far made out, labelling the parts in 

 the sketch. 



Now lay out the parts already studied, taking care not to 

 injure the delicate membranes by which they are held in position. 

 See how the various viscera are attached to the dorsal wall of 

 the metacoele by membranes (mesenteries). Are these mesenteries 

 continuous or interrupted? Make out the following regions in 

 them: (1) a mesogaster attached to the stomach; (2) a mesentery 

 proper, supporting the large intestine; and (3) amesorectum with 

 similar relations to rectum and rectal gland. 



Also make out similar membranes (omenta) connecting por- 

 tions of the digestive tract to each other: (1) a gastro-hepatic 

 omentum connecting the stomach and liver; (2) a gastro-splenic 

 omentum extending from stomach to spleen ; and (3) an hepato- 

 duodenal omentum between the liver and duodenum. In these 

 mesenteries and omenta trace the following blood-vessels. 



Arteries. The most anterior of these, the cceliac axis, emerges 

 from the dorsal wall of the body cavity in the middle line, passes 

 to the right of stomach and enters the hepato-duodenal omentum, 

 where it divides into gastro-hepatic and anterior intestinal 

 arteries. The gastro-hepatic almost immediately divides into 

 hepatic (going to the liver) and gastric arteries, the latter supply- 

 ing the cardiac end of the stomach. Trace the anterior intestinal 

 artery backwards to the pylorus, noting the twigs to the pylorus 

 and the duodenal artery to the duodenum. How does the main 

 trunk pass the pancreas to reach the ventral surface of the large 

 intestine? Notice the branches of this intestinal portion following 

 the lines of insertion of the spiral valve. Do any of them make 

 the complete circuit of the intestine? How far back on the 

 intestine does this anterior intestinal artery extend? 



The superior mesenteric artery arises from the mid-dorsal 

 line in the posterior two thirds of the body cavity, dividing almost 

 immediately into an anterior gastro-splenic artery and a posterior 



