THE FROG : VISCERA AND VASCULAR SYSTEM 59 



is the dorsal aorta. It runs backwards immediately be- 

 low the backbone, giving off paired renal arteries to the 

 kidneys, ovarian or spermatic arteries to the generative 

 organs, and a small median posterior mesenteric artery to 

 the rectum, after which it divides into two iliac arteries to 

 the legs and abdominal muscles. 



The blood from the lungs is returned by the right and 

 left pulmonary veins, through a short common pulmonary 

 vein to the left auricle. From the rest of the body the blood 

 is returned to the sinus venosus by three large veins, the 

 right and left superior vena cava or precaval veins in front, 

 and the median inferior vena cava or postcaval vein behind. 

 Each precaval is formed by the junction of three veins, the 

 external jugular, innominate, and subclavian. The external 

 jugular is fed by a lingual vein from the floor of the mouth 

 and a mandibular from the lower jaw. The innominate 

 arises by the junction of an internal jugular from the head 

 and a subscapular from the shoulder and back of the arm. 

 The subclavian receives the brachial from the arm and the 

 great musculo-cutaneous from the skin, the mucous membrane 

 of the mouth, and many head and trunk muscles. The 

 inferior vena cava arises by the junction of several renal 

 veins from the kidneys and ovarian or spermatic veins 

 from the generative organs, and, just before it enters 

 the sinu«, is joined by two hepatic veins from the liver. 

 Blood is returned from the legs by a^ femor al vein on the 

 outside and a sciatic on the insidelof each limb. Each 

 femoral vein divides on reaching the trunk into a renal 

 portal and a pelvic. The former receives the sciatic and 

 runs to the kidney, just before entering which it receives 

 the dorsolumbar vein from some of the muscles of the back. 

 In the kidney the vein breaks up into capillaries, which are 

 collected, with those of the renal artery, to give rise to the 

 renal veins. Thus it comes about that much of the blood 

 in the renal veins has passed through two sets of capillaries, 

 one in the leg and another in the kidney. Such an arrange- 

 ment, in which the blood having passed through one set of 

 capillaries is then sent through a second, is called a. portal 

 system. The pelvic veins of the two sides lie in the abdominal 

 wall and join to form the anterior abdominal vein which runs 

 forwards above the linea alba in the middle of the belly (see 



