SCYLLIUM CANICULA 243 



of the hinder end of the pancreas. It then leaves the gut wall and, 

 passing through the mesentery, enters the posterior corner of the 

 gland, uniting as it does so with the posterior lieno-gastric vein, a 

 trunk coming from the bend of the stomach and the spleen. In 

 this way is constituted the main hepatic portal vein, which then runs 

 up embedded in the dorsal edge of the pancreas to its anterior end, 

 where it receives two large tributaries. The first of these is the 

 gastro-intestinal vein formed by factors coming from the pyloric end 

 of the stomach and the spleen adjacent thereto and the front end 

 of the intestine and a fairly large ultra-intestinal vein which lies right 

 in the central axis of the spiral valve, and so is not readily seen save 

 in a section. The second vessel is the dorsal anterior gastric vein 

 formed in the main by the union of a branch from the dorsal side 

 of the front end of the stomach and one from the oesophagus. The 

 main hepatic portal vein now leaves the pancreas and runs through 

 the gastro-hepatic omentum, where it is joined by a ventral anterior 

 gastric vein of similar constitution to the dorsal vessel, but coming 

 from the ventral side of the oesophagus. Finally it divides into right 

 and left branches feeding the corresponding lobes of the liver. 



The blood from the liver is taken up by two short efferent hepatic 

 veins, one coming from the anterior end of each lobe of the liver. 

 They almost immediately unite to form a large single hepatic sinus, 

 which communicates with the ventro-posterior wall of the sinus 

 venosus through the pericardio-peritoneal septum by two separate 

 openings indicative of its double origin. 



The ductus Cuvieri in the adult appears as a tube projecting a 

 short distance into the post-cardinal sinus, wherein it opens by a 

 spout-like aperture. It passes inwards on the ventro-lateral wall of 

 the oesophagus through a conspicuous notch in the posterior border 

 of the fifth cerato-branchial cartilage and on into the pericardial 

 cavity, where it is continuous with the sinus venosus. Thus it will 

 be seen it is the vessel by which the whole of the blood is returned 

 to the heart, save only that brought from the liver by the hepatic 

 sinus. 



In the embryo the veins have not yet swollen up to form 

 sinuses, so that their anatomical relationships are somewhat clearer. 

 The anterior and posterior cardinal veins on each side join together 

 at the level of the sinus venosus to form the ductus Cuvieri, and so 

 both open into it. This, the primitive arrangement, is afterwards 

 masked by the enormous enlargement of the two trunks so that, as 

 noticed above, the anterior sinus opens into the posterior one and 

 the ductus Cuvieri appears as a tube projecting into the latter. At 

 a very early stage the anterior vein is one continuous vessel only, 

 but at a somewhat later stage the part of it in front of the point 



