Vascular System of Bdellostoma dombeyt. 33 
THE PoRTAL VENOUS SYSTEM. 
The portal venous system includes the portal vein and all 
the vessels which flow into it. 
The anterior portal vein (Figs. XVII, XVIII, XIX, ap) 
arises in the right branchial region, a little in front of the 
posterior end of the “club-muscle.” (Fig. XIX.) It lies just 
below and to the right of the notochord, and receives the 
somatic veins from the right side in the branchial region. A 
few scattering venous twigs from this region also pass across 
into the inferior jugular vein. ‘The anterior portal continues 
backward into the fold (portal septum), separating the inner 
and outer chambers of the right pericardial cavity, as pre- 
viously described. It passes between the alimentary canal 
and the right pronephros, and opens into the roof of the 
portal heart near the anterior end. ‘The entrance is guarded 
by a pair of thin membranous valves, semi-lunar in shape, 
one anterior and one posterior. (See Fig. XVI, ap.) Just 
before entering the portal heart it receives a branch which is 
made up of a twig from the pronephros, and (often) two or 
three somatic veins lying opposite and posterior to the portal 
heart. In one instance, I observed an anastomosis between 
this vein and a somatic vein emptying into the right posterior 
cardinal vein. 
The supra-intestinal vein (Figs. XI, XII, XV, XVII, 
XVIII, XIX, supr. int.) receives the blood from the entire 
intestinal wall, excepting the floor in the anterior region. It 
runs forward just above the intestine a little to the right of 
the median line, within the mesentery. It lies to the right of 
the vagus nerve and the mesenteric arteries. In the region 
of the reproductive organs the supra-intestinal vein receives 
several genital veins which descend in the mesentery. These 
veins are formed by the plexus of small venous twigs in the 
special genital fold of the mesentery (Figs. XII, XVIII, 
gen). On reaching the pericardial region, the supra intes- 
tinal vein turns to the right side of the intestine. Here it 
receives the cystic vein (Fig. XIX, cv), which is made up of 
branches from the gall cyst. The supra-intestinal vein then 
passes through the pericardio-peritoneal foramen, beside the 
intestine, and below the right mesonephros. It then crosses 
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