74 ALLEN | 
muscle of the caudal fin. When the caudal fin is reached this 
artery bifurcates into a dorsal and a ventral vessel, which run 
dorsad or ventrad in the basal canal of the caudal rays, directly 
in front of the corresponding lymphatic and venous vessels. 
The central canal of each ray receives a branch, which at first 
runs in the center of the cavity and then divides, the 2 forks 
continuing caudad along the dorsal and ventral sides of the 
canal. 
Throughout its entire course the dorsal aorta gives off 
branches to the great lateral muscles, the spinal cord, and the 
rays of the unpaired fins; beside supplying the kidney, repro- 
ductive organs and the rectum. 
(a) Arteries Supplying the Great Lateral Muscle, Cord, 
etc.—Perhaps the most typical place first to take up these ves- 
sels is in the region of the caudal vertebre. In fig. 1 sucha 
region is shown just posterior to the kidney. The common 
arrangement consists of a dorsal or neural artery and a ventral 
or hemal artery, which usually supply the region covered by 
2 myotomes; sometimes, however, one of these arteries may 
supply 3 or even 4 myotomes. 
The dorsal or neural arteries (Pl. I, fig. 1; Neu.A.) in this 
region arise from the dorsal side of the caudal artery. Emerg- 
ing from the anterior surface of the hamal arch each neural 
artery curves around the anterior end of either the right or left 
side of the centrum. Here a branch, the medzan lateral artery 
(fig. 1; M.Lat.A.) is given off to the great lateral muscle. A 
second branch, the spznal or myelon artery, penetrates the spinal 
foramen. The neural artery then curves around in front of 
the neural spine and continues dorsad between the spine and 
the neural lymphatic vessel. Near the end of the spine the 
dorsal lateral artery (fig.1; D.Lat.A.) is given off to the great 
lateral muscle. Then passing cephalad the neural artery sup- 
plies the levator and depressor muscles of this and the preced- 
ing dorsal rays, as well as supplying the superficial muscles 
and sending up a branch behind this and the preceding dorsal 
rays. This description will hold for all the neural arteries 
from the head to the tail, except that the most cephalic one 
arises from a different source (see under Subclavian artery), 
