Vascular System of Bdellostoma dombeyt. 29 
XVII, XVIII, scd) arising on each side of the head. It 
leaves the cranium just dorsal to the corresponding vagus 
nerve. It passes backward alongside the vagus, between the 
lateral trunk muscles, and the constrictors of the pharynx. 
In this region it receives the first eight or ten somatic veins. 
These somatic veins, like the somatic arteries (with which 
they alternate), arise from the skin and trunk muscles the 
entire length of the body. ‘They correspond exactly to the 
somatic veins of the abdominal region shown in Figure XV, 
(s). They are each composed of a very short terminal trunk 
which is supplied by two branches, (1) a dovsa/ branch which 
collects the blood from the dorsal region of the integument, 
the spinal cord, notochord and muscles of the vicinity. It 
descends vertically at the side of the notochord, and on 
reaching the ventral surface of the dorsal body wall, joins 
with (2) the ventral branch, or “‘znztercostal”’ vein. ‘The in- 
tercostal veins, like the intercostal arteries, are distributed 
to the integument of the ventral and lateral regions of the 
body, and the ventral rectus muscle. In the gill region, the 
intercostals receive, in the region of the slime glands, 
occasional “pleural’’ branches from the connective tissue. 
Then after collecting the blood from the two adjacent slime 
glands, it passes between these along the intermuscular 
septum of the myotomes, on the ventral surface of the dorsal 
and dorso-lateral body walls. The intercostal veins lie just 
in front of the corresponding intercostal nerves. As before 
mentioned, the intercostal veins usually alternate with the 
intercostal arteries (Figs. XI, XII, XV, XIX, ic), especially 
in the abdominal region. In the pharyngeal region the 
arrangement is less regular, there being often two adjacent 
arteries or veins, and occasionally both an artery or vein on 
one intermuscular septum. (Fig. XIX.) After receiving the 
somatic veins from the head region, the superficial cardinal 
pierces the constrictor muscle and joins the deep cardinal 
vein. 
The deep anterior cardinal vein (Figs. XVII, XVIII, ded) 
arises from the integument and muscles of the anterior head 
region. It passes on each side between the pharynx and 
hyoid arch (just below the posterior process), then directly 
backward alongside the pharynx, internal to the constrictors, 
17 
