494 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 hemal 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, Pl. II.) almost closes a bony foramen with 
the spines. Asa rule, the right branch distributes itself entirely at 
this point by dorsal and ventral 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, Pl. II.) to the tail-fin. 
The fin rays consist of two separate halves, each half bemg 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 
vertebree, 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 fin 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 hzemal 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. 
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