26 THE HUMAN MECHANISM 



large intestine. The supply to the legs has already been 

 mentioned. Other small arteries arise from the abdominal 

 aorta and are distributed to the muscles 

 and skin of the back. The arteries to the 

 stomach and intestine lie in the mesen- 

 tery (Fig. 163) and their course may 

 .be readily traced in a dissection. 



18. The course and branches of the 

 venae cavae. The blood which has thus 

 been distributed from the aorta returns 

 to the opposite side of the heart through 

 the veins which ultimately form the two 

 vense cavae. In general, it may be stated 

 that the veins of those organs which are 

 anterior to the diaphragm form the su- 

 perior vena cava, while those posterior 

 to the diaphragm form the inferior vena 

 cava. The larger veins usually run near 

 and approximately parallel to the larger 

 arteries. This is the case with those 

 from the arms and legs, the kidneys, 

 and the muscles of the trunk. One nota- 

 ble and very important exception, how- 

 ever, is found in the venous supply of 

 the stomach, spleen, and intestines, the 

 veins of which unite to form a single 

 large vein (portal vein) which passes 

 to the liver, where it breaks up into 

 smaller vessels; the blood which has 

 thus passed through the liver is finally 

 collected in the hepatic vein and poured 

 by this into the inferior vena cava just 

 before the latter passes through the dia- 

 phragm on its way to the right ventricle 

 FIG. 18. Nerve trunks J 



of the right arm (Fig. 15; see also Ing. 70). 



