BLOOD-VASCULAR SYSTEM OF THE LORICATI 107 
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’ Vern (P\. I, figs. 1, 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 right 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 /eft caudal vein. The latter vessel (figs. 1 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 /eft caudal vern (figs. 1 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 hemal 
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 hemal spine. 
Each neural vein (fig. 1; 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 
