THE ARTERIES. 357 



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. 



/?. 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. 



The next two arteries may be better seen during the dis- 

 section of the neck. If dissected now, the greatest care must 

 be taken not to injure the nerves (see fig. 65, p. 374). 



ii. The right carotid artery runs forwards along- 

 side the trachea, supplying the neck. The 

 ramus descendens of the hypoglossal nerve 

 crosses it. Opposite 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. 



b. The left subclavian artery arises from the left side 



of the arch of the aorta : its course and branches 

 correspond to those of the right subclavian. 



c. The intercostal arteries are a series of small paired 



arteries, arising from the dorsal surface of the 

 aorta, and running outwards on the inner sur- 

 face of the thoracic walls, one behind each rib. 



3. Arteries arising from the aorta in the abdomen. 



In examining these arteries the mesentery must not be cut. 

 a. The cceliac artery is a large median vessel, arising 

 from the ventral surface of the aorta, about half 



