504 



ANATOMY OF VERTEBRATES. 



332 



portal vein : this dilates and describes a spiral curve on entering 

 the liver, and has a valvular structure ensuring the onward flow 

 of blood to the elongated gland, during the compression exercised 

 in the contortions of the Snake. The hepatic veins enter the 



j^ostcaval, and this large trunk 

 terminates in the hind end of 

 the long auricular sinus. 



The blood from the head and 

 fore-part of the body is re- 

 turned to the fore-part of the 

 sinus by a jugular vein and an 

 inferior azygos vein, each of 

 which has a pair of valves at 

 its termination : and by a su- 

 perior azygos vein, which has 

 three valves at its termination: 

 there is a fourth vein, answer- 

 ing to the left precaval, which 

 passes behind the left auricle 

 to terminate in the right sinus 

 auricula? near the postcaval 

 orifice : it receives the coronary 

 vein before its termination. 



In Lacertians the blood 

 from the liind limbs is partly 

 conveyed by a reni-portal 

 vein, fig. .3.32, K, to the kid- 

 neys, and partly by a trunk, 

 which communicates with the 

 caudal vein to an umbilical 

 or sub-abdominal vein, L : this, 

 as it advances, collects blood 

 from the ventral walls of the 

 trunlc, and receives a recur- 

 rent thoracic vein : it then 

 communicates with the trunk 

 of the gastro-intestinal, pan- 



Olrculatioii III aLiznra{Xr(aii'/ 0C(7/a^(). CCI.XVU. CrCatic and Sl^louic VoluS 



to form the great portal vein which penetrates the liver. The 

 renal veins, li, unite to form the postcaval, v, which afterwards 

 receives the hepatic veins, and proceeds to the auricular sinus. 

 A small cardinal or azygos vein, returning part of the blood 

 from the tail, advances along the back part of the abdominal 



