4O THE FROG 



1. Veins that enter the anterior venae cavae. 



(a) The external jugular entering anteriorly is formed 

 by the union of the lingual vein, conveying blood from the 

 floor of the mouth and the tongue, and the mandibular vein, 

 running ventral to the lower jaw. 



(b) The innominate vein entering laterally is formed by 

 the union of the internal jugular, conveying blood from 

 the interior of the skull, and the subscapular, conveying 

 blood from the dorsal side of the arm and the shoulder. 



(c) The subclavian vein, entering laterally and pos- 

 teriorly, is formed by the union of the brachial vein, return- 

 ing blood from the arm, and the musculo-cutaneous vein, 

 a large vein running in the skin along the side of the body 

 and returning blood from the skin and muscles of the dorsal 

 and lateral regions of the trunk and head. 



2. Veins that enter the posterior vena cava. 



(a) The hepatic veins from the liver enter the posterior 

 vena cava not far from the sinus venosus. 



(&) The renal veins from the kidneys pass straight 

 toward the middle line and form by their union the begin- 

 ning of the posterior vena cava. 



(c) The genital (ovarian or spermatic) veins from the 

 ovaries or testes, according to the sex, lead into the posterior 

 vena cava, either directly or by uniting with renal veins. 



3. The portal systems. A portal system may be denned 

 as a system of veins which carries blood from one network 

 of capillaries to another in an entirely different organ. 

 There are two portal systems in the frog : the renal portal 

 system carrying blood from the hind limbs to the kidneys, 

 and the hepatic portal system conveying blood from sev- 

 eral sources to the liver. 



