VENOUS SYSTEM 225 



cardium, the sinuses of the two sides narrow 

 considerably, and run back side by side to the 

 hinder end of the body-cavity, lying between 

 the kidneys, from which they draw blood by 

 numerous renal veins. The right sinus extends 

 quite to the hinder end of the kidneys, but 

 the left usually commences further forwards. 



SUt open the ventral walls of both sinuses at their anterior 

 ends, and wash out the blood ; note the enormous size of the 

 sinuses and their free communication with each other, dorsal 

 to the oesophagus. Follow the right sinus bach to its com- 

 mencement between the posterior ends of the kidneys, slitting 

 open its ventral wall, but avoiding injury to the cloaca. 



At its anterior end, immediately to the 

 outer side of its opening into the Cuvierian 

 sinus, the posterior cardinal sinus receives 

 the subclavian vein, which returns blood 

 from the pectoral fin and adjacent parts of 

 the body- wall, and runs in a groove along the 

 inner surface of the pectoral girdle. A little 

 way further back it receives the lateral vein, 

 which runs in the body-wall alongside the 

 lateral line ; and further back stLU, just behind 

 i the point where the oesophagus passes between 

 the two posterior cardinal sinuses, each of 

 these latter has on its ventral surface the 

 opening of the genital sinus, which surrounds 

 the reproductive gland. 



2. The renal portal system. 



The blood from the tail is returned by the candal 

 vein, which lies below the caudal artery in the 

 haemal arches of the vertebrae. 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. 



