CHAP. IX.] 



THE VASCULAR SYSTEM. 



97 



are separated from each other by only a narrow interval, corre- 

 sponding 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. 



The external carotid has eight 

 branches, which are distributed 

 to the throat, tongue, face, and 

 walls of the cranium. 



The chief branches of the in- 

 ternal carotid are the ophthalmic 

 and cerebral arteries. A remark- 

 able anastomosis exists between 

 the cerebral arteries at the base of 

 the brain. The arteries are joined 

 in such a manner as to form a 

 complete circle, and this anasto- 

 mosis, known as the " circle of 

 Willis," both equalizes the circula- 

 tion of the blood in the brain, and 

 also provides, in case of destruction 

 of one of the arteries, for the blood 

 reaching the brain through the 

 other vessels. 



The subclavian arteries. The 

 right subclavian arises at the 

 division of the innominate, and 

 the left subclavian from the arch 

 of the aorta. The subclavian 

 arteries are the first portions of a 

 long trunk which forms the main 

 artery of the upper limb, and which 

 is artificially divided for purposes 

 of description into three parts; OF THB ARTERIES OF THE A KM, 



viz. the subclavian, axillary, and ^S^^SLSSMS^ 



bracMal arteries. The Subclavian artery; 6, deep palmar arch; 8, ulnar 



artery passes a short way up the arter y- 



thorax into the neck, and then turns downwards to rest on the 



first rib. At the outer border of the first rib it ceases to be called 



FIG. 74. DEEP ANTERIOR VIEW 



