THE HEART AND ARTERIES OF POLYODON 



447 



ward and backward in an intermuscular septum. This branch 

 ramifies somewhat in the septum but maintains its individuahty 

 until it reaches the lateral line where it divides into dorsal and 

 ventral branches and shows some inclination to anastomose 

 with similar vessels in front and behind it. The main stem next 

 gives off a spray of small vessels to the notochordal sheath and 

 higher up a branch that enters the spinal canal. Beside the 

 neural spine there arises a second lateral branch very much 



Fig. 18 Diagramatic cross section in the region of the kidney 



like the first. Dorsally the parietal artery itself ends in a ter- 

 minal bifurcation, or, in the region of the dorsal fin, becomes one 

 of the arteries of supply to that structure. In a fish about a 

 meter long there were five pairs of dorsal arteries to the fin. 



The splanchnic arteries (fig. 18, a. spl.) may give off small 

 ventral branches to the air-bladder, kidney or gonad, lateral 

 to which they continue ventrally close to the peritoneum. They 

 show a slight tendency to anastomose and form longitudinal 

 connecting vessels below. Several of them supply each ventral 



