DISTRIBUTION OF ARTERIES. 113 



substance. From the axillary artery spring all the arteries 

 of the fore extremity. This vessel can only be seen by 

 detaching the shoulder from the body. It arises within the 

 chest, from the arteria innominata ; gains exit by making a 

 sudden turn around the first rib, rather below its middle, cross- 

 ing 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 afterwards takes 

 the name of the brachial artery. Its branches are — 1. The 

 external thoracic. 2. The humeral thoracic, which runs to the 

 point of the shoulder, and gives its branches to the levator 

 humeri and shoulder joint. 3. The dorsalis scapula? ascends, 

 in a flexuous manner, to the shoulder joint, crossing the inser- 

 tion of the subscapularis. It runs for a short distance along 

 the ribs. 4. The subscapularis, a large artery, which also arises 

 from the upper part of the trunk, but near to its termination. 

 It passes along the ribs, screened from view by the edges of 

 the subscapularis and teres major, to both of which muscles 

 it detaches several small branches, and ends near the lower 

 angle of the bone ; it also gives off several branches to the 

 triceps and panniculus. 



The humeral artery descends from the inner and back part 

 of the head of the os humeri, in an oblique direction on the 

 body of the bone, where it divides into the ulnar, spiral, and 

 radial arteries. On its inner side, it has the spiral and ulnar 

 nerves ; in front, the radial nerve ; and behind, the hume- 

 ral veins ; and it is covered internally by the large pectoral 

 muscle, 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 enters the muscle called triceps. 3. Near its 

 termination, another branch to the flexor brachii. Where the 

 artery divides, it is covered by the humeral plexus of veins, 

 and by the absorbent glands of the arm. 



The ulnar artery consists of a common root, from which 

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