THE ARTERIES 319 



the aorta, runs backwards through the thorax and 

 abdomen. It lies on the ventral surface of the 

 vertebral column, and divides about an inch in front 

 of the level of the pubic symphysis into the two 

 common iliac arteries. 



2. Arteries arising from the aorta in the thorax. 



a. The innominate artery arises from the commence- l 

 ment of the arch of the aorta : it gives off, close 

 to its origin, the left carotid artery, and then runs 

 forwards a short distance and divides into the 

 right subclavian and right carotid arteries. 



i. The right subclavian artery" runs outwards just i/ 

 in front of the first rib : it gives branches to 

 the shoulder, and runs on as the brachial 

 artery into the right fore-limb. Its principal 

 branches are the following. 



a. The vertebral artery arises from the sub- 

 clavian just beyond its origin, and passing 

 dorsalwards enters the vertebrarterial canal 

 of the cervical vertebrae, along which it 

 passes, supplying the spinal cord and the 

 brain. 



/3. The internal mammary artery arises from the 

 subclavian just before it leaves the thorax, 

 and runs backwards along the inner surface 

 of the ventral wall of the thorax. 



ii. The right carotid artery runs forwards along- 

 side the trachea, supplying the neck. Oppo- 

 site the angle of the jaw it divides into (1) the 

 internal carotid artery, which enters the skull 

 through the carotid foramen to supply the 

 brain; and (2) the external carotid artery, 

 which supplies the right side of the head and 

 face. 



iii. The left carotid artery corresponds to the 

 right carotid in its course and distribution. 



