Vascular System of Bdellostoma dombeyt. 21 
By) is 3 
vein, it continues backward a little below and to the left of 
the median ventral aorta. (Fig. X.) It receives a varying 
number of branches from the body wall. It also receives 
several small “pleural” twigs from the connective tissue and 
gill passages, including the oesophago-cutaneous duct and 
the adjoining pharyngeal wall. Finally, the inferior jugular 
vein empties into the anterior end of the sinus venosus, just 
in front of the sinu-auricular aperture. 
The posterior cardinal veins arise in the caudal region from 
small twigs which form two small veins. These lateral veins 
accompany the arteries on each side of the cartilaginous 
median ventral plate in the caudal region. (Fig. XVII.) 
They unite to form the median caudal vein (caud), which 
runs forward immediately beneath the caudal artery. The 
caudal vein, at its posterior end, is dilated to form a small 
sinus just in front of the median ventral plate. Laterally, 
the caudal vein receives, on each side, the somatic veins of 
the caudal region. 
Anteriorly, in the cloacal region, the caudal vein divides 
into two veins, the r7ght and left posterior cardinal veins. 
(Figs. XI, XII, XV, XVIII, XIX, pcr, pel.) These vessels 
run parallel with each other, just below and on each side of 
the posterior dorsal aorta. The right posterior cardinal is 
much smaller than the left. (See Figs. XII, XV, XVII.) 
Each lies internal to and in contact with that side of the 
corresponding mesonephros which faces toward the median 
line. The posterior cardinals are joined by a large number 
of short transverse commissural vessels (about twenty-five in 
all). They are not placed at regular intervals, but are more 
numerous in the posterior region. They vary in size, being 
usually about as wide as the right cardinal vein. The 
posterior cardinals receive two sets of branches: (1) the 
renal branches; (2) the somatic veins. 
The renal branches (see Fig. XII), appear to arise, for the 
most part, on the ventral surface of the mesonephros. They 
collect together and form small twigs, which run across 
toward the median line and empty into the corresponding 
posterior cardinal vein. ‘These renal veins are somewhat 
irregularly distributed, but traces of their original segmental 
arrangement are easily recognized. 
19 
