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situated beneath tho limb. In their thoracic portion, tho brachial trunks 

 at first lying beside each other, separate slightly in front to roach the internal 

 face of each of tho two first ribs. They are accompanied by tho cardiac, 

 pneumogastric, inferior laryugeal, and diaphragmatic nerves, and are in- 

 cluded, as already noticed, between tho two layers .of tho anterior medias- 

 tinum. The right occupies nearly tho median line beneath the inferior faco 

 of the trachea, to tho left and above tho anterior vena cava. The left 

 slightly rises on tho side of the trachea, and generally corresponds inwardly 

 to the thoracic duct. 



In their axillary portion, these vessels accompany the corresponding 

 venous trunks, cross tho terminal tendon of the subscapularis muscle in 

 passing below the humeral insertion of the pectoralis magnus, and among 

 the branches of the brachial plexus, but embraced more particularly by 

 the median, anterior humeral, and ulnar nerves. 



Distribution. The axillary arteries give off, on their course, eight col- 

 lateral branches. Four arise from the thoracic portion : three upper, tho 

 dorsal, superior cervical, and vertebral arteries ; and an inferior, the intrr,ttil 

 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 axillary portion of the trunk and pass upwards : they are 

 the super- and subscapular arteries. After furnishing the latter vessel, the 

 brachial trunk is continued by the humeral artery. 



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

 near its origin, tho common trunk of tho two carotid arteries, which will bo 

 studied in a separate article. 



Ireparation. Tho subject being placed on the right tide, remove the skin and th 

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



Firtt p ri<><L Dissect nil the intra-thoracic portion of the left axillary artery and its 

 collateral branches, as in figure 282, taking care to leave the inferior cervical art ry (which 

 has been cut in the figure to render the drawing more distinct) attached by its MIJM -iiur 

 extremity to tlie middle portion of the mastoido-humeralis, which has not lx; n di.-iurl < d. 



Second period. Prepare, on the separated limb, the extra-thoracic puti-n of tho 

 vessel and all the arteries it furnishes, in taking as guides figures 283, 290, and 2U1. 



COLLATERAL BRANCHES OF THE AXILLARY ARTERIES. 



1. Dorsal, Dorso-muscular or Transverse Cervical Artery. (Fig. 282, 4.) 



Chiefly destined to tho muscles of the withers, this artery, tho first given 

 off by the brachial trunk, crosses outwardly tho trachea, thoracic duct, 

 oesophagus, great sympathetic nerve, and tho long muscle of tho neck, in 

 proceeding beneath the mediastinal layer ; it reaches and passes over tho 

 second intercostal space, bends slightly backwards, and places itself in tho 

 interstice which, separates the angular muscle of tho scapula and great 

 serratus muscle from the inferior branch of tho ilio-spinal muscle (longis- 

 simus dorsi), where it separates into several divergent branches. The majority 

 of these ascend towards tho superior border of the withers, neck, and 

 shoulders, by gliding between tho latter muscles, the splenius, and tho 

 small anterior serratus on the one part, and tho great scrratus, rhomboidem, 

 and proper elevator of the shoulder on tho other, to bo distributed to those 

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

 branches passes between tho splcnius and tho great complexus muscles, 

 parallel with the superior cervical artery, which is in front of it. and com- 

 municates by its minuscules with the latter vessel, as well as with the 

 vertebral and occipito-inuficular arteries. The last-named branch is some- 



