172 ESSENTIALS OF ZOOLOGY 



supply the brain. A vertebral artery, also from the first 

 branchial, reaches the brain by way of the vertebral column. 



The dorsal aorta gives off a pair of subclavian arteries 

 just before it receives the last pair of efferent branchials, and 

 then in succession a series of median arteries which run in the 

 mesentery of the peritoneal cavity. These are the coeliac, 

 supplying the stomach and liver ; anterior mesenteric, directed 

 to the pancreas, spleen, and intestine ; and the posterior mesen- 

 teric, which gives blood to the rectal gland. Paired vessels 

 are supplied to the reproductive organs, kidneys (renal), and 

 to the pelvic fins (iliac), and then the aorta passes on into the 

 tail as the caudal artery. The blood is conveyed by all these 

 branches into capillaries, and these reassemble to form veins. 



The blood from the tail is returned by the caudal vein. 

 The caudal vein bifurcates on entering the body to form two 

 renal portal veins. These veins, after receiving branches 

 from the pelvic fin and body wall, send branches into the 

 kidneys. The kidneys thus receive both arterial and venous 

 blood, and this blood is carried away by the renal veins. The 

 renal veins open into the posterior end of the posterior cardinal 

 veins, which lie along the inner border of the kidney and are 

 connected at their posterior ends by an anastomosing branch. 

 In front of the kidney the posterior cardinals fuse to form an 

 expansive cardinal sinus. This sinus receives the blood from 

 the reproductive organs on each side by large openings which 

 transmit the blood from the reproductive sinus spermatic or 

 ovarian, according to sex. The two cardinal veins emerge again 

 in front, and are directed forwards and outwards to open into 

 the precaval or Cuvierian sinus. 



The precaval sinus opens into the sinus venosus of the heart, 

 and it receives besides other important vessels : 



(1) The lateral vein brings blood from the pelvic fin. Pos- 

 teriorly it is directed forwards in the mesentery to enter the 

 cardinal sinus in company with its neighbour, and this portion 

 of the vessel is called the haemorrhoidal. The rest of the vessel 

 is regarded as a fusion of the epigastric and the brachial, 

 which latter enters the precaval sinus at its anterior end. 



(2) The blood from the liver is received into a hepatic 

 sinus which opens into the precaval sinus on each side. 



