Parker. — Anatomy and Embryology of Scyrnnus lichia. 225 



3. Circulatory organs. 



The heart is comparatively small, not more than half the size of that of 

 a porbeagle (Lamna cornubica), a few inches longer than the specimen under 

 consideration ; this is probably correlated with the small size of the pec- 

 toral fins. Owing to various unfavourable circumstances — the chief of 

 which was the necessity of preserving the skin uninjured for stuffing — I was 

 unable to make a thorough examination of the arteries and veins, and have 

 therefore but few observations to record. 



The blood-supply of the alimentary canal presents some points of in- 

 terest. As a general rule the splanchnic arteries consist of two of about 

 equal size, the coeliac and the anterior mesenteric springing close together 

 from the dorsal aorta and supplying between them the greater part of the 

 canal as well as the liver, pancreas, and spleen, and of a small posterior 

 mesenteric supplying the rectum. 



In Scyrnnus, on the other hand, there is only a single main artery, the 

 coeliac (figs. 2 and 3, cce.a), which sends off a hepatic branch, and runs 

 backwards along the right side of the stomach, parallel to the bile-duct and 

 portal vein, supplying the left side of the stomach as it goes ; it then passes 

 to the dorsal side of the bursa Entiana, and curves round the latter to reach 

 the ventral aspect of the intestine ; forming then the duodenal artery (du. a) 

 which takes a spiral course round the ventral and left sides of the gut, send- 

 ing off transverse branches to its walls, as well as the intra-intestinal 

 artery presently to be described. The coeliac also gives off, near the 

 pylorus, a small left gastric artery (g. a), which curves round the posterior 

 border of the stomach, and then passes straight forward along its left side. 



The rest of the alimentary canal is supplied by no less than three mesen- 

 teric arteries, an anterior (fig. 3, a. m. a), a middle (m. m. a), and a posterior 

 [p. m. a) ; all are small arteries proceeding straight from the dorsal aorta to 

 the right side of the intestine, and forming between them a longitudinal 

 vessel, which runs parallel to the mesenteric vein (m. v), sends off transverse 

 branches to the right side of the intestine, and takes altogether a spiral 

 course, so that its distal end comes to lie on the ventral wall of the gut 

 (fig. 2, p. m. a). The anterior mesenteric, which is the largest of the three, 

 gives off a lieno-gastric artery {I. g. a), which gives branches to the spleen 

 and is continued up the left side of the stomach. 



The blood is returned from the intestine by two veins, the duodenal 

 (chi.v) and the mesenteric (m.v), which pass forward with a turn to the 

 right and unite with one another close to the pylorus to form the portal 

 vein (fig. 3, p. v) : the duodenal runs alongside the artery of the same name 

 (du.a), the mesenteric alongside the longitudinal branches of the mesenteric 

 arteries. The duodenal vein receives transverse veins from the intestinal 

 15 



