THE ELASMOBRANCH FISHES 229 



ing freely with one another above it. The posterior cardinal 

 sinus of each side opens into the ductus Cuvieri by a relatively 

 narrow passage situated below and behind the opening of 

 the anterior cardinal sinus, and just behind and to the outer 

 side of this passage it receives the subclavian vein bringing 

 back blood from the pectoral fin, and a little further back is 

 the opening of the lateral sinus, a vessel which runs up the 

 side of the body clos^ to the surface and in connection 

 with the lateral line, and curves inwards and downwards 

 past the scapula to enter the posterior cardinal sinus. The 

 opening of the genital sinus is placed still further back, 

 just above and to the side of the oesophagus. 



The blood from the tail is collected into a caudal vein 

 which lies below the caudal artery enclosed in the canal 

 formed by the haemal arches of the caudal vertebras. On 

 reaching the hinder ends of the kidneys the caudal vein 

 divides right and left to form the veins of Jacobson, also 

 called the renal portal veins. These run forward along the 

 dorsal edges of the kidneys, are joined by the intercostal veins 

 of that region, and give off branches to them throughout their 

 entire length. These branches break up again into capillaries 

 in the kidneys, and the blood is collected from these 

 capillaries by the renal veins and passed into the posterior 

 cardinal sinuses. Thus the dogfish, like the frog (vol. i. 

 p. 56), has a renal portal system. The blood from the 

 stomach, intestine, and spleen is collected by (i) the posterior 

 intestinal vein (fig. 51, /.#.); (2) the posterior gastric vein 

 (p.g.v.) ; and (3) the splenic vein (s.p.v.}. These vessels unite 

 together to form the mesenteric vein, which runs forwards 

 along the dorsal border of the pancreas, and receiving an 

 anterior intestinal and an anterior gastric vein becomes 

 the hepatic portal vein, which runs forward alongside the 

 bile duct and enters the liver, where it branches and breaks 

 up into capillaries. The blood from the liver is collected 

 into two large sinuses traversing the right and left lobes of 

 the liver, and these run forwards to form a pair of wide hepatic 

 sinuses separated by an incomplete partition on the ventral 

 wall of the oesophagus. The hepatic sinuses open by two 

 small apertures into the sinus venosus opposite the opening 

 of the latter into the auricle. It should be noticed that a 

 hepatic portal system is present in Amphioxus as well as in 



