424 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



The art. cuadalis terminates by dividing beneath the second last 

 centrum into two branches, which pass upwards and backwards on 

 the sides of the last centrum beneath its haemal spines, which are 

 widened by being attached to small lateral processes on the lower 

 portion of the body so as to afford space and protection for these 

 vessels. A horizontal ledge of bone which projects from each side 

 of the spine A (Fig. 5, PI. II.) almost closes a bony foramen with 

 the spines. As a rule, the right branch distributes itself entirely at 

 this point by dorsal and venti*al branches to the deep muscles of the 

 caudal fin, and branches along the surface of the flat spines to its 

 intrinsic muscles. The left branch, however, after giving off similar 

 vessels sends a large branch along the dorsal surface of the bony 

 ledge and thence in the median line between the spines B and C, 

 (Fig. 5, PI. II.) to the tail-fin. 



The fin r-ays consist of two separate halves, each half being con- 

 vex on its outer surface and deeply grooved on the inner. They are 

 attached by their base on each side of the flat spines of the bodyless 

 vertebrae, and so form an arch in which a canal runs the entire 

 width of the fin. The artery upon entering this canal divides into 

 a dorsal and a ventral stem, from which a branch passes out between 

 the halves of each ray, or several of these branches may arise by a 

 common stem. The artery in the ray usually divides into two 

 which run parallel to each other. 



In sections of the tin a layer of connective tissue is seen to 

 occupy the median plane passing between the halves of the rays 

 where it forms a median canal for the arteries and two lateral canals 

 for the veins. 



The short rays of the dorsal margin are supplied by the arteries to 

 the muscles mentioned above. The dorsal and ventral fins, with 

 their musculature, are supplied by two or three of the ordinary 

 spinal arteries somewhat enlarged at these points. 



The art. renales are given off from the haemal vessels passing 

 around the kidney, of which there are usually three or four pairs 

 specially enlarged. The most posterior of these is continued to the 

 pelvic fins entering on the posterior surface. A large branch is also 

 continued forward to the muscles attached to the pelvic arch. The 

 arrangement of the vessels in the caudal fin may be taken as repre- 

 sentative of what occurs in the others. 



