THE CIRCULATION. 155 



a little cartilaginous nodule called the nodule of Arantius, 

 or corpus Arantii. These may possibly serve to make the 

 edges fit more perfectly. The manner in which these valves 



Fig. 73. THE SEMILUNAR VALVES OF THE AORTA. (Allen Thomson.) 

 , l>, c, the individual pouches. 



act may be easily demonstrated on a beef's heart by open- 

 ing the ventricles until the semilunar valves in question are 

 exposed, and then pouring water down the pulmonary artery 

 or the aorta toward the heart. In so doing the semilunar 

 pouches as distended, meet in the center, and prevent the 

 progress of the liquid. 



THE DISTRIBUTION OF THE VESSELS OVER 'THE BODY. 



1. The Arterial Stream. It is the aorta which springs 

 from the left ventricle of the heart from which all the sys- 

 temic arteries take their origin. The first arteries branch- 

 ing off, are the two coronary arteries of the heart, which 

 leave the aorta just above the semilunar valves. The aorta 

 then makes a turn to the left, and descends through the 

 chest and abdomen. From the arch of the aorta several im- 

 portant arteries arise. The first is the innominate artery 

 which at once divides into the subclavian, which goes to 

 the arm, and into the right common carotid, which goes to 

 the head. From the right subclavian springs the intra- 

 vertebral artery which goes to the head, passing through the 

 intra- vertebral foramina of the cervical vertebrae. The com- 

 mon carotid divides into an external carotid and an internal 

 carotid, the former going to the face and scalp, the inner 

 to the brain. A little to the right of the origin of the in- 

 nominate artery the left common carotid leaves the arch of 

 the aorta. In its branching and destination it is the same 



