GUIDES FOR VERTEBRATE DISSECTION 



turn. That part of the mesentery which supports the hinder end 

 of the intestine is the mesorectum. 



Now examine the extent of the body cavity. It is lined every- 

 where by a smooth membrane, the peritoneum, which also covers 

 mesenteries and viscera so that all organs really lie outside the 

 peritoneum. In front note that the body cavity is bounded by 

 a thin membrane, the false diaphragm or septum transversum. 



Various blood-vessels course in the mesenteries and omenta. 

 Make out the following, drawing them in a separate sketch as 

 you proceed, the arteries in red, the veins in blue. 



In the middle line of the dorsal wall of the coelom is the 

 large artery, the dorsal aorta. From this arise several arteries. 

 In the mesogaster is the gastric artery, which soon branches and 

 supplies both sides of the stomach. Which of the branches, 

 right or left, gives off twigs (splenic artery) to the spleen? 



Posterior to the gastric artery are segmental intercostal 

 arteries leading into the muscles of the back, and, in the female, 

 more numerous and smaller arteries supplying the oviducts. 



At about the middle of the ccelom the dorsal aorta gives off, 

 into the mesentery, a cceliac axis which soon divides into a 

 gastro-splenic artery, going to the stomach and spleen, and a 

 hepato-pancreatic artery, which supplies not only the pancreas 

 and liver but sends branches to the stomach as well. 



The intestine is supplied by several (how many?) mesenteric 

 arteries each of which branches in the mesentery into fine twigs 

 (intestinal arteries) which enter the intestinal walls. 



The mesenteric vein runs in the mesentery parallel to the 

 intestine. It is formed by the union of numerous intestinal veins 

 from the intestinal wall, and is to be traced forward, through the 

 pancreas, receiving a pancreatic vein in its course, to its union 

 with the gastro-splenic vein to form the hepatic portal vein which 

 enters the liver near the bile-duct. The gastro-splenic vein is 

 formed by the union of gastric and splenic veins coming from 

 stomach and spleen respectively. The hepatic portal vein runs 

 for some distance along the dorsal surface of the liver and is rein- 

 forced in its course by a ventral abdominal vein which passes 

 dorsally from the ventral body wall. Trace the branches of the 

 portal vein on and in the liver. 



A second vein, the postcava (vena cava inferior) extends 

 from about the middl of the dorsal surface of the liver dorsally 



