SUBCLAVIAN. 



137 



the pons varolii, giving ^^S- ^^^• 



off several branches in 

 its course. The princi- 

 pal being the superior 

 cerebellar'' and the poste- 

 rior cerebral arteries.^ 



The posterior com- 

 municating^ joins the 

 carotid with the posterior 

 cerebral. 



From the carotid, which 

 enters through the carotid 

 canal, are given off the 

 ophthalmic :^^ middle ce- 

 rebrals^ and anterior ce- 

 rebral arteries .^^ The two 

 anterior cerebral arteries 

 are connected by a trans- 

 verse branch^^ called the 

 anterior communicating 

 artery, and thus is form- 

 ed the circle of Willis. 

 These vessels are distri- 

 buted to the ^:»za mater , 

 and the substance of the 

 brain. 



SUBCLAVIAN. 



The subclavian^ of the right side arises from the innominata,* and 

 the subclavian of the left side from 

 the arch of the aorta. The right is 

 shorter and more superficial than the 

 left. The subclavian emerges from 

 the thorax by passing over the first 

 rib between the anterior and middle 

 scaleni muscles. Its branches are 

 usually five in number. Some of 

 which arise by a common origin^ 

 called the thyroid axis. 



Vertebral,^ is the first and largest 

 branch of the subclavian. It passes 

 through the foramina of the trans- 

 verse processes of the six superior 

 cervical vertebroe, and enters the ca- 

 vity of the cranium through the fora- 

 men magnum occipitis. 



Fig. 119. 



12^ 



