Chap. 24.] 'Arteries (f tie Head. 24^ 



orbit, and which communicates with twigs of the ex- 

 ternal carotid about the face. 



The internal carotid afterwards runs under the bafe 

 of the brain at each fide of the infundibulum, where 

 it is at a fmall diftance from the carotid artery of the 

 other fide. At this part it commonly divides into two 

 branches, one of which pafles towards the anterior, 

 the other towards the pofterior part of the brain, 

 where it communicates with the vertebral artery of the 

 fame fide. The arteries of the brain are inclofed in 

 the folds of the pia mater, and are not diftributed on 

 the fubitance of the brain itfelf, till after having under- 

 gone a minute divifion. 



The fubclavian arteries are fo called, becaufe they 

 pafs under or behind the clavicles. Each fubclavian 

 artery fends off a confiderable one to the internal parts 

 of the head. They proceed from the upper and pof- 

 terior part of the fubclavian, and obtain the denomina- 

 tion of the vertebral arteries, becaufe they pafs through 

 openings in the tranfverfe procefles of the vertebrse of 

 the neck. Having reached the great foramen of the 

 os occipitis, they enter the cranium, and pierce the 

 dura mater. The two vertebral arteries, after they 

 have entered the cranium, gradually advance towards 

 each other, and at length unite, forming the arteria 

 bafilaris. 



The fubclavian. artery alfo fends off twigs to 

 the mediaftinum, ftiymus, trachea, and pericardium. 

 It alfo fends off two branches of a larger fize, called 

 the mammaria interna, and cervicalis, befides the vcr- 

 tebralis, which has been already defcribed. 



The fubclavian artery, where it leaves the thorax, 



immediately above the firft rib, changes its* name to 



that of the. arteria axillaris, becaufe its pafles under the 



axilla. In this courfe it gives off four principal 



Rj branches, 



