BLOOD-VESSELS OF MUSTELTTS ANTAROTIOUS. 
709 
imbedded one in the right the other in the left lobe, and opening anteriorly into 
the hepatic sinus [Hep. S.). 
The latter is a capacious chamber lying immediately cephalad of the liver and 
ventrad of the oesophagus. When distended with blood or injection it completely 
fills the antero-ventral region of the coelome, abutting in front against the pericardio¬ 
peritoneal septum ( Peric. perit. Sept.), while posteriorly it adapts itself to the 
anterior border of the liver. Its general relations to surrounding parts are best 
seen in transverse and horizontal sections of a frozen fish (Plate 35, fig. 9 ; Plate 37, 
figs. 19, 20, and 21). 
Internally the hepatic sinus is divided into right and left compartments by an 
incomplete vertical partition ( p) formed of an irregular network of fibrous trabeculae. 
Each compartment is also traversed by numerous irregular fibrous bands. The 
hepatic veins open each into the compartment of its own side by a large aperture. 
The hepatic sinus opens into the sinus venosus by two small circular apertures 
(Ilep. S'.), placed close together in its anterior wall one on each side of the median 
partition. 
It will be seen from the above description that the relations of the “ system of the 
sub-intestinal vein ” to the embryonic trunk from which it takes its origin is 
remarkably clear in Mustelus antarcticus. We have, first, the caudal vein, the 
relations of which are only disturbed by the atrophy of the post-anal gut; this is 
followed, after a short interruption of continuity, by the intra-intestinal, which is 
directly continued into the main portal vein ; then the continuity of the original 
vessel is again interrupted, this time by the capillaries of the liver, following which 
we have the paired hepatic veins opening by the hepatic sinus into the heart. There 
is thus a successive series of longitudinal trunks, all unpaired, except the hepatic 
veins, indicating, in the adult, the course of the originally continuous sub-intestinal 
vein of the embryo. 
In this, as in so many points, the Sharks exhibit a more generalized type of 
structure than the Rays. Besides the retention of a large intra-intestinal vein in 
many Selachians, the hepatic sinus in Raja has no direct communication with the 
sinus venosus, but opens by two widely separated apertures into the two precaval 
sinuses (see 16 and 21, or 23). 
