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 vertebras. In fig. i such a 

 region is shown just posterior to the kidney. The common 

 arrangement consists of a dorsal or neural artery and a ventral 

 or haemal arter}?-, 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. i ; Neu.A.) in this 

 region arise from the dorsal side of the caudal artery. Emerg- 

 ing from the anterior surface of the haemal arch each neural 

 artery curves around the anterior end of either the right or left 

 side of the centrum. Here a branch, the median lateral artery 

 (fig. I ; M.Lat.A.) is given off to the great lateral muscle. A 

 second branch, the spinal ox niyelon 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. i ; 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), 



