252 THE DOG-FISH. 



iii. The posterior cardinal sinus extends back along 

 the dorsal surface of the abdominal cavity 

 close to the median plane, its dorsal wall being 

 firmly united to the body-wall, and its ventral 

 surface covered by the peritoneum. Its 

 anterior end forms a very large thin-walled 

 sac, three-quarters of an inch or more in 

 width. In front ib lies at the side of the 

 oesophagus, and close to the hepatic sinus ; 

 further back it lies dorsal to the oesophagus, 

 and alongside its fellow of the other side, with 

 which it communicates freely. Behind this 

 point, i.e. about two inches behind the peri- 

 cardium, the sinuses of the two sides narrow 

 considerably, and run back side by side to 

 the hinder end of the abdominal cavity, lying 

 between the kidneys, from which they draw 

 blood by numerous renal veins. The right 

 sinus extends to the hinder end of the kidneys, 

 but the left usually commences further for- 

 wards. 



Slit 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. Pass a seeker backwards along the right sinus 

 to its commencement between the posterior ends of the kidneys 

 {fig. 52) ; but do not lay it open in this hinder part, lest the 

 reproductive organs and the cloaca should be injured. 



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. There are 

 two pairs of lateral veins. One pair arises 

 from the pelvic region and runs forward to 



