CIRCULATORY SYSTEM. 183 



Axillary Artery, 



The source from which is derived all the arteries sup- 

 plying THE rouE EXTREMITY. This vcsscl is SO buricd be- 

 tween the scapula and the trunk, that not only is it out of the 

 way of all injury, but is excluded from all possibility of being got 

 at for the purpose of demonstration without detaching the limb 

 from the side. It arises within the chest from the arteria inno- 

 minata, and gains exit by making a sudden turn around the first 

 rib, rather below its middle, crossing the lower border of the 

 scalenus in the turn : it is first directed outward in this flexure, 

 and then backward, and at length reaches the inner part of the 

 head of the humerus, where it makes another turn backward, and 

 subsequently takes the name of humeral artery. Its branches 

 are — 1. The external thoracic extends backward across the arches 

 of the ribs, taking the same course as the vessel called the " spur 

 vein," and supplying the muscles thereabouts. 2. The humeral 

 thoracic runs to the point of the shoulder, and gives its branches 

 to the levator humeri and shoulder-joint. 3, The dorsal is sca- 

 pula ascends in a flexuous manner obliquely upon the shoulder- 

 joint, crossing the insertion of the subscapularis ; it next runs 

 for a short way along the anterior costa, around which it subse- 

 quently continues to reach the antea-spinatus. 4. The subscapu- 

 laris, a large artery arising from the upper part of the trunk, but 

 near to its termination, creeps upward along the posterior costa, 

 screened from view by the edges of the subscapularis and teres 

 major, to both of which muscles it detaches laterally several 

 small branches, and ends near the posterior angle of the bone. 

 It gives off a considerable branch at a short distance from its 

 origin, which proceeds in a waving line across the inner surface 

 of the triceps, and ends in the panniculus carnosus ; and another, 

 a deep-seated one, about the middle of the costa, which is prin- 

 cipally expended in the head of the triceps. 



The HUMERAL ARTERY desccuds from the inner and back 

 part of the head of the os humeri in an oblique direction to the 

 inferior and anterior part of the body of the bone, where it splits 

 into the ulnar, spiral, and radial arteries. To its inner side run 

 the spiral and ulnar nerves ; in front, the radial nerve ; and be- 

 hind, the humeral veins : and it is covered internally by the pec- 

 toralis magnus, to which it sends some small branches. But its 

 principal branches are — 1. One near its origin which crosses the 

 bone to get to the flexor brachii, and sends twigs to the shoulder- 

 joint. 2. A posterior branch, arising a little lower down, which 

 bifurcates and then enters the triceps, 3. Near its termination, 

 another anterior branch passes to the flexor brachii. In the 



