BLOOD-VASCULAR SYSTEM OF THE LORICATI IO7 



cephalad through the center of this organ ; it follows the right 

 fork of the kidney and unites with the right jugular to form the 

 right precava. Throughout its course it receives numerous 

 branches, which will be described in detail later on. There is 

 also a smaller left cardinal for the left lobe of the kidney, 

 which will also be considered under a separate head. 



(a) Caudal Vein (PI. I, figs, i, 7, 8, 9 and 10; Cau.V.).— 

 This trunk has its origin in the region of the last vertebra from 

 a right and left branch ; both of which have a more superficial 

 course than the corresponding arteries. The rig/it caudal 

 vein (fig. 7, R. Cau.V.) is much the shorter; it arises from 

 the region of the tail and passes cephalad between the super- 

 ficial and profundus muscles, and when the last vertebra is 

 reached, curves inward, and after receiving a dorsal branch 

 joins the larger left caudal vein. The latter vessel (figs, i and 

 7 ; L. Cau.V.) has its origin from a dorsal and a ventral branch 

 in the caudal fin ray canal. These branches lie immediately 

 behind the corresponding lymphatic and arterial vessels. They 

 receive a branch from the central canal of each ray, coming 

 from the fin membrane and the fin ray muscles. Uniting be- 

 tween the two hypural bones the dorsal and ventral branches 

 form the left caudal vein (figs, i and 7, L. Cau.V.), which 

 passes cephalad between the superficial and profundus caudal 

 fin muscles, receiving branches from each. In the region of 

 the last vertebra it receives a dorsal branch and curves inward 

 to unite with the right caudal vein, but before joining the left 

 caudal vein to form the main caudal vein, each of the caudal 

 veins appears to receive a vessel from the caudal lymphatic 

 sinus. The course of the caudal vein is cephalad in the haemal 

 canal, immediately below^ the caudal artery; and in its course 

 to the kidney receives a dorsal branch from in front of each 

 alternate neural spine, and a ventral branch from in front of 

 each alternate haemal spine. 



Each neural vein (fig. i; Neu.V.) has its origin from a 



. cephalic and a caudal branch ; the latter returns the venous 



blood from superficial and profundus levator and depressor 



muscles of that ray ; while the former returns the blood from 



the corresponding muscles of the preceding ray, and each 



