SANGUIFEROUS SYSTEM. 501 



cipal trunk of the iliac vein on each side, the course of the 

 superficial veins on the legs and arms imitating in some 

 degree their distribution in quadrupeds. After receiving the 

 haemorrhoidal, the emulgent, the caudal, the hypogastric, the 

 spermatic, and other veins of the pelvis, the two iliacs unite 

 to form the inferior cava, which in advancing to the heart, 

 receives the trunks of numerous distinct hepatic veins which 

 emanate from behind the liver, and the inferior cava forms 

 the same capacious sinus in diving birds as in other diving 

 animals. The smaller branches of the inferior cava anas- 

 tomose freely with the mesenteric veins proceeding to form 

 the vena portre of the liver, and others, advancing from the 

 posterior part of the pelvis, form two trunks which penetrate 

 the kidneys, and appear to form a renal portal circulation to 

 contribute to the secretion of these organs. The principal 

 part of the venous blood however, from the chylopoietic 

 organs, from the spleen, the pancreas, the stomach and intes- 

 tines, is collected into the great trunk of the portal vein, to 

 be transmitted with the blood of the hephatic artery, through 

 the lobes of the liver, and by the free communications of 

 these two portal systems, the renal and the hephatic, they 

 are capable of relieving each other, as well as the inferior cava, 

 the sinus venosus, and the heart. 



The venous blood is returned from the hand and fore-arm 

 chiefly by two veins, which unite at the bend of the arm to form 

 the humeral vein, and these vessels accompany the correspond- 

 ing arteries, but in a more superficial position. The axillary or 

 subclavian vein on each side, after receiving the superficial 

 and deep-seated branches around the shoulder and fore part 

 of the trunk, unites with the jugular and vertebral vein to 

 form the superior vena cava of its respective side. The 

 vertebral vein of each side anastomoses freely at the exterior 

 of the base of the skull with the branches of the single jugular 

 vein, and accompanies the vertebral artery and cervical por- 

 tion of the sympathetic, through the canal of the transverse 

 processes, receiving the blood from the sinuses of the brain, 

 the cervical portion of the spinal chord, and the back parts 

 of the neck. The jugular veins are single on each side, and 

 anastomose freely with each other, as well as with the ver- 

 tebral veins, below the base of the skull, so that a free 

 circulation is provided for under the various circumstances 



