Chap. XI] 



THE VASCULAR SYSTEM 



191 



external carotid, (2) the internal carotid. At the root of the neck 

 the common carotids are separated from each other by only a 

 narrow interval, corresponding with the width of the trachea ; 

 but as they ascend they are separated by a much larger interval, 

 corresponding with the breadth of the larynx and pharynx. 



Each external carotid has eight branches, which are distributed 

 to the throat, tongue, face, ears, and walls of the cranium. 



Fig. 121. — Subclavian and Axillary Arteries. (Gerrish.) 



Each internal carotid has many branches which are distributed 

 to the brain and eyes. The chief ones are the cerebral and 

 ophthalmic. 



Circle of Willis. — The circle of Willis is a remarkable anastomosis 

 formed by the blood-vessels of the brain. It is situated at the base 

 of the brain and is formed by the union of (1) the anterior and 

 posterior cerebral arteries, which are branches of the internal 

 carotid, and (2) branches of the basilar artery, which is formed by 



