230 THE DOG-FISH 



2. The renal portal systen?. 



The blood from the tail is returned by the caudal 

 vein, which lies below the caudal artery in the 

 hsemal arches of the vertebra. Opposite the hinder 

 end of the kidneys the caudal vein divides into the 

 right and left renal portal veins, which run forwards 

 along the dorsal edges of the right and left kidneys 

 respectively, receiving branches from the body-wall, 

 and supplying the kidneys along their whole length. 



The dissection of the renal 'portal system should he post- 

 poned till after that of the urino-genital system, in order to 

 a/ooid damaging the cloaca. 



Gut across the tail about two inches behind the cloaca. 

 Find the caudal vein lying in the hcemal arches of the vertebrce, 

 ventral to the caudal artery ; trace the vein forwards with a, 

 seelcer, or inject it, and then dissect it out. 



3. The hepatic portal system. 



The hepatic portal vein is formed by the union of 

 two veins, one from the main lobe of the spleen and 

 the other from the intestine. It runs forwards in the 

 mesentery along the dorsal border of the pancreas ; 

 and, receiving veins from the pancreas and from the 

 stomach, enters the liver a little to the right of the 

 median plane. 



Find the hepatic portal vein at the point where it enters 

 the liver, a little to the right of the junction of the two lobes, 

 and follow it backwards, turning aside the viscera as may be 

 necessary, but not cutting anything. 



0. The Arterial System. 



The arterial system may conveniently be described under 

 three heads : (1) the afferent branchial vessels, which carry 

 the venous blood from the heart to the giUs to be purified ; 

 (2) the efferent branchial vessels, which collect the purified 

 blood from the gills ; and (3) the dorsal aorta, which is formed 

 by the union of the efferent branchial vessels, and conveys 

 arterial blood to the body generally. 



