THE BRACHIAL OR AXILLARY ARTERIES. 645 



brachial plexus, but embraced more particularly bj the median, anterior humeral, 

 and uljiar nerves. 



Distribution. — The axillary arteries give off, on their course, eight collateral 

 branches. Four arise from the thoracic portion : three upper — the dorsal, 

 superior cervical, and vertebral arteries ; and an inferior — the internal thoracic. 

 Two are detached at the first rib — one downwards, the other forwards ; these are 

 the external thoracic and superior cervical arteries. Two originate from the axil- 

 lary portion of the trunk and pass upwards : they are the supra- and subscapular 

 arteries. After furnishing the latter vessel, the brachial trunk is continued by the 

 humeral artenj. 



Independently of all these branches, the right axillary artery gives off, near 

 its origin, the common trunk of the two carotid arteries, which will be studied in 

 a separate article. 



Preparation. — The subject being placed on the right side, remove the skin and the left 

 anterior limb, in order to make the dissection at two periods. 



First period. — Dissect all the intra-thoracic portion of the left axillary artery and its col- 

 lateral branches, as in Fig. 375, taking care to leave the inferior cervical artery (which has 

 been cut in the figure to render the drawing more distinct) attached by its superior extremity 

 to the middle portion of the mastoido-humeralis, which has not been disturbed. 



Second period. — Prepare, on the separated limb, the extra-thoracic portion of the vessel and 

 all the arteries it furnishes, in taking as guides Figs. 376, 377. 



Collateral Branches of the Axillary Arteries. 

 1. DoESAL, DoRSO-MUSCULAE, OE Teansveese Ceevical Aetery (Fig. 375, 4). 



Chiefly directed to the muscles of the withers, this artery — the first given off 

 by the brachial trunk — crosses outwardly the trachea, thoracic duct, oesophagus, 

 great sympathetic nerve, and the longus colli, in proceeding beneath the media- 

 stinal layer ; it reaches and passes over the second intercostal space, bends slightly 

 backwards, and places itself in the interstice separating the angularis scapulse 

 and serratus magnus from the inferior branch of the longissimus dorsi, where it 

 separates into several divergent branches. The majority of these ascend towards 

 the superior border of the withers, neck, and shoulders, by gliding between the 

 latter muscles, the splenius, and the serratus anticus on the one part, and the 

 serratus magnus and rhomboideus on the other, to be distributed to those 

 muscles and the integuments covering them. The most anterior of these 

 branches passes between the splenius and complexus muscles, parallel with 

 the superior cervical artery, which is in front of it, and communicates by its 

 ramuscules with the latter vessel, as well as with the vertebral and occipito- 

 muscular arteries. The last-named branch is sometimes long and voluminous, 

 and partly supplements the superior cervical, as is exemplified in the specimen 

 which served for Fig. 375. 



Before leaving the thorax, the dorsal artery gives off some unimportant 

 ramuscules and the subcostal artery {superior intei-costal of Man). This branch 

 (Fig. 375, 5) curves backwards and, with the sympathetic chain, places itself 

 beneath the costo-vertebral articulations, against the longus colli, furnishing the 

 second, third, and fourth intercostal arteries and the corresponding spinal branches, 

 and terminating at the fifth intercostal space by either forming the artery which 

 descends into that space, in anastomosing by inosculation with a branch emanat- 

 ing from the first posterior intercostal artery, or by expending itself in the spinal 



