316 FISHES CHAP. 
in certain features than is the case in any other group. The pre- 
caudal portion of the subintestinal vein retains much of its original 
importance and runs in the rudimentary intestinal spiral valve as 
far as the liver, where it becomes the hepatic portal vein. From 
the liver the blood is collected into a single hepatic vein, and by it 
is conveyed to the sinus venosus. The caudal section of the sub- 
intestinal vein, now known as the caudal vein, bifureates near the 
anus, and its two branches become directly continuous with the 
right and left posterior cardinals, without forming a renal portal 
system. In their forward course to the heart the posterior cardinals. 
are situated directly beneath the notochord, and after receiving 
the blood from the kidneys and gonads, and from the numerous 
pairs of segmental veins of the body-wall, join the corresponding 
anterior cardinal veins, and form on each side a short transverse 
Cuvierian duct which opens into the sinus venosus. There is 
also a pair of inferior jugular veins which, however, unite opposite 
the fifth pair of gill-sacs to form a single trunk; this vessel is 
continued backwards, externally to the medio-ventral cartilage of 
the branchial basket, and finally opens directly into the sinus 
venosus. 
In Elasmobranchs (e.g. Mustelus antarcticus) ' the caudal vein 
(Fig. 186) lies in the haemal canal of the caudal portion of the 
vertebral column. On reaching the kidneys the vein divides into 
two renal portal veins, which, however, are not directly continuous 
with the posterior cardinal veins as in the Cyclostomata, but, 
on the contrary, after receiving the posterior segmental and 
oviducal veins, become continuous with the capillaries of the 
kidneys. 
From the latter organs the blood is collected by a series of 
renal veins, and by them conveyed to the posterior cardinals, and 
thence to the Cuvierian ducts. In the adult, therefore, there is 
a well-developed renal portal system, but it is worthy of note, 
nevertheless, that this system is developed comparatively late in 
embryonic life, and that at an earlier stage the caudal vein is 
directly continuous with the two posterior cardinals, precisely as: 
is the case in the Cyclostomata throughout life. The posterior 
cardinal veins are situated in the dorsal wall of the coelom (Fig. 
187), beneath the vertebral column. For the hinder portion of 
'T. Jeffery Parker, Phil. Trans. 177, Pt. ii. 1886, p. 702. For references to: 
Elasmobranchs in general, see Parker, op. cit. p. 725. 
