BLOOD-VASCULAR SYSTEM, ETC., OF AMIURUS CATUS. 423 



posterior end. This vessel passes directly downward through the 

 substance of the kidney to the mesentery, and anastomosing with 

 the left mesenteric artery is distributed with it to the rectum. 



The descending aorta behind the origin of the cceliaco-mesenteric 

 artery enters a deep groove (PI. IV., Fig. 7) on the ventral surface 

 of the fourth vertebra to pass the attachment of the air-bladder. 

 Throughout the rest of its course in the body-cavity it lies upon the 

 rounded surfaces of the centra. In the tail as the art. catidalis it 

 occupies the bottom of a groove on the centra, and is further pro- 

 tected by the haemal arches and by the short spines which arise from 

 the sides of the groove between these arches. A longitudinal dorsal 

 ridge projects into its lumen as in some other forms. 



The arteries given off to the trunk and tail arrange themselves in 

 three sets, neural, lateral and haemal. Each pair of neural and 

 lateral branches arise by common stems, which, passing around the 

 vertebra, give off the lateral arteries about the middle of the centrum, 

 and are then continued upwards along the posterior surface of the 

 neural spine as the neural arteries. 



The lateral arteries pass outwards by the division in the lateral 

 trunk musculatui'e along the 'lateral line,' giving branches to these 

 muscles. 



The neural arteries divide into branches which run between the 

 lateral muscles and supracarinales, and branches which pass upwards 

 in the median line between the supracarinales. 



The hcemal arteries have similar relations to the ventral muscles. 

 They arise independently, and run upon the anterior surface of the 

 haemal spine. Throughout the length of the body cavity these 

 arteries (intercostales) ran with the nerves between the peritoneal 

 lining and the muscles of the body wall. 



These vessels present the same irregularity in Amiurus as is found 

 in other Teleostei. A large number have entirely disappeared or 

 been greatly reduced in size, and the blood is distributed by large 

 single stems, now from the right side and now from the left, giving 

 branches to both sides of the body and spreading over from two to 

 five myomeres. 



The lateral arteries and the haemal arteries of the body cavity can, 

 from their position, supply only one-half of the body, and conse- 

 quently present greater regularity than the others. 



