THE HEART AND ARTERIES OF POLYODON 449 



in a free strand of tissue, it descends along the anterior face of 

 the air-bladder nearly to the cardiac end of the oesophagus, a 

 distance of about a decimeter in a fish a meter long. Throughout 

 the greater part of this portion of its course it is closely envel- 

 oped between the air-bladder and the dorsal aspect of the right 

 lobe of the liver, making a deep furrow in the later. On the 

 right side near the junction of the oesophagus and stomach 

 it gives off its first large branch, the coeliac division (figs. 13, 19, 

 a. coe.), and comes into relation with the portal vein. Asso- 

 ciated with the vein in a free strand, it passes under the oeso- 

 phagus to the right side of the intestine to which it gives a few 

 branches and then enters the spleen which it supplies copiously. 

 Emerging behind, dorsally and somewhat to the right it gives 

 off a few small branches which go to the rectum, and a large 

 one which enters the mesentery and bifurcates, one division 

 going to the fundus of the stomach and the other to the pos- 

 terior ventral aspect of the air-bladder where it anastomoses 

 with the dorsal arteries to that organ. This casual anastomosis 

 may become important for, in one specimen, the main blood 

 supply to the whole posterior part of the alimentary canal came 

 down through the channel thus opened up, making a kind of 

 anomalous posterior mesenteric artery. Behind the spleen the 

 main vessel (a.rec.) is continued in the median line down the 

 dorsal side of the rectum to which it gives off several branches, 

 and, at least in some cases, becomes directly continuous and 

 also anastomoses indirectly with some of the posterior ventral 

 segmental arteries. 



The coeliac division of the artery gives rise first to oesophageal 

 branches, some of the anterior of which may send twigs to the 

 swim-bladder above and the liver below. At about the same 

 level there also arises a slender artery (a.he.p.) to the liver which 

 • often .reaches as far as the gall-bladder. This is the principal 

 right posterior hepatic artery. The main vessel, subject to 

 considerable variation, gives rise to branches to all the neigh- 

 boring organs and then turns dorsally in the angle on the right 

 side of the gastro-intestinal junction. As it approaches the 



