COMPARATIVE ANATOMY OF THE CIRCULATORY SYSTEM 219 



laterally at the point where the lateral vein enters the common cardinal vein, 

 the subclavian artery gives rise to the ventral abdominal artery which proceeds 

 posteriorly halfway between the lateral vein and the midventral line. This 

 artery is somewhat irregular in the smooth dogfish but conspicuous in the spiny 

 dogfish and skate. It gives off branches segmentally into the body wall and at 

 the posterior end of the pleuroperitoneal cavity anastomoses with the vessels 

 supplying the pelvic fins. After giving off these branches into the body wall 

 the subclavian artery, now named the brachial artery, proceeds into the pec- 

 toral fin. 



The dorsal aorta is a very large vessel situated in the mid-dorsal line of the 

 pleuroperitoneal cavity. It has median unpaired visceral or splanchnic branches 

 to the viscera, lateral visceral branches to the urogenital system, and somatic 

 branches to the body wall. The median visceral branches are as follows. Work 

 on the left side turning the viscera to the right. 



Spiny dogfish: Just after it has penetrated the pleuroperitoneal cavity, the 

 dorsal aorta gives rise to the large coeliac artery which distributes blood to the 

 gonads, stomach, and liver. Near its origin the coeliac artery gives off small 

 branches into the adjacent gonads, esophagus, and cardiac end of the stomach. 

 It then runs posteriorly for a considerable distance without branching; it enters 

 the gastrohepatic ligament and gives rise to three branches: the gastric, the 

 hepatic, and the pancreatico-mesenteric artery. The gastric artery passes to the 

 stomach and divides into dorsal and ventral gastric arteries which branch on 

 the surface of the stomach and penetrate its walls. The hepatic artery turns 

 anteriorly, runs alongside the bile duct, and enters the substance of the liver. 

 The pancreatico-mesenteric artery passes dorsal to the pylorus, gives off small 

 branches into the pyloric portion of the stomach and the ventral lobe of the 

 pancreas, a moderately large duodenal artery into the duodenum, and a large 

 anterior mesenteric artery along the right side of the small intestine to which it 

 gives off branches at the rings of attachment of the spiral valve. The dorsal 

 aorta after giving rise to the coeliac artery runs without further visceral branches 

 to the free edge of the dorsal mesentery. Here it gives off two arteries which 

 course in the border of the mesentery. One of these, the gastrosplenic artery, 

 passes to the spleen and bend of the stomach. The other vessel is the superior 

 mesenteric artery. It passes to the small intestine and, as the posterior mesenteric 

 artery, runs posteriorly on the left side of the intestine with branches correspond- 

 ing to those of the anterior mesenteric. Beyond the gap in the dorsal mesentery, 

 the dorsal aorta gives off the inferior mesenteric artery which passes along the 

 free anterior border of the mesorectum into the rectal gland. 



Smooth dogfish: Shortly after entering the pleuroperitoneal cavity, the 

 dorsal aorta gives rise to the large coeliac artery. This has small branches into 

 the adjacent gonads and soon divides into gastric and pancreatico-mesenteric 

 arteries. The gastric artery immediately forks into a smaller anterior gastric 



