LEPIDOSIREN PARADOXA. 
121 
loses its direct communicatiou with the sinus venosus and 
breaks up into capillaries in the liver substance (Text-fig. 
26 c, 1. lat. V. V ,) . 
At the same time the left lateral vitelline vein becomes 
connected with the venous spaces appearing in the spleen 
and pancreas, while it is still continuous round the dorsal wall 
and left side of the gut with the subintestinal vein. The 
anterior or hepatic segment of the subiutestinal vein now 
disappears (Stage 35) as far back as its junction with 
with the left vitelline vein, so that the hinder persistent part 
of the subintestinal vessel (Text-fig. 26 n. Si. V.) loses its 
direct connection with the liver and sinus venosus, which it 
now reaches by means of its anastomosis round the left side 
of the gut with the left vitelline vein (Text-fig. 26 n, 1. lat. 
V. V.). The lateral vitelline vein arches round the gut 
parallel with the insertion of the spiral valve, and at its junc- 
tion veutrally with the subiutestinal vein a tributary vein 
.(Text-fig. 26 E, /S'p. V.) emerges on the opposite side of that 
vessel, and passing round the gut, follows the line of inser- 
tion of the spiral valve and fuses with the subiutestinal vein 
at each point where it crosses the mid-ventral line. 
This vein of the spiral valve therefore forms a series of 
diminishing spiral coils that are united veutrally by the sub- 
intestinal vein (Text-fig. 26 e, Si. F., F). Behind the 
spiral valve the subintestinal vein tapers off in the region of 
the anus. The portal system is thus formed by the left 
lateral vitelline and subintestinal veins and their tributaries 
that pass into the left side of the liver anteriorly, where 
they form a vascular channel extending along the left 
margin of that organ (Text-fig. 26 E, H. F. F). This lateral 
•channel appears with the formation of the portal system, and, 
passing back along the margin of the liver, breaks up into 
capillaries in its substance, from which numerous hepatic 
radicles convey the blood to the posterior vena cava. The 
development of the subintestinal (portal) vein with its tri- 
butary vessel from the spiral fold essentially resembles that 
■of the same two vessels in the elasmobranch (20), except that 
