198 THE CIRCULATORY APPARATUS 



The circle of Willis is situated at the base of the 

 brain, it is an anastomosis formed by the bloodvessels 

 of the brain. The arteries entering into its formation 

 are: In front, the two anterior cerebral arteries, 

 branches of the internal carotid, which are connected 

 by the anterior communicating artery ; behind, by two 

 posterior cerebral arteries, branches of the basilar, and 

 these communicate latterly with the internal carotids 

 through the posterior communicating arteries. 



The Arteries of the Upper Extermity. THE AXILLARY 

 ARTERY. The axillary artery is the continuation of 

 the subclavian. It extends from the lower border of 

 the first rib, where it is deeply placed, to the lower 

 border of the teres major tendon, where it is super- 

 ficial, and there becomes the brachial. It is described 

 in three parts the first, above the pectoralis minor; 

 the second, behind it; and the third, below it. 



Branches. First part, superior and acromial thoracic; 

 second part, long and alar thoracic; third part, sub- 

 scapular and circumflex, posterior and anterior. 



THE BRACHIAL ARTERY. The brachial artery extends 

 from the end of the axillary, at the lower border of 

 the teres major, to \ inch below the elbow-joint, divid- 

 ing into the radial and ulnar arteries. 



The branches of the brachial artery are : The superior 

 profunda, nutrient artery, to the humerus, the inferior 

 profunda, anastomotica magna, and muscular.. 



THE RADIAL ARTERY. The radial artery runs from 

 the bifurcation of the brachial along the radial side 

 of the forearm to the wrist, and winds back to its pos- 

 terior surface. It then enters the palm through the 

 first dorsal interosseous, and runs across the hand to 

 form the deep palmar arch by joining the deep branch 

 of the ulnar, and gives off in the ball of the thumb the 

 superficialis volse, a branch which joins with the main 

 termination of the ulnar artery to form the superficial 

 palmar arch. 



