DI8SBCTI0N OF THE ANTERIOR LIMB. 5 



point as the preceding, but from the opposite side of the parent vessel ; 

 and, passing backwards in relation to the axillary surface of the deep 

 pectorals, it distributes branches to these, and also to the superficial 

 pectorals. A slender branch from it accompanies the subcutaneous 

 thoracic vein to the panniculus carnosus. 



The Axillary Vein is the upward continuation of the brachial vein, 

 and is at its lower part posterior to the artery ; but at the anterior 

 border of the first rib it is below the artery, and it here joins the 

 jugulars and the axillary vein of the opposite side, thus forming the 

 anterior vena cava. 



Birections.—The axillary vessels may now be cut as they turn round 

 the first rib, and the limb may be further adducted to facilitate the 

 dissection of the brachial plexus, which, in its first step, should be 

 undertaken by the dissectors of the limb and of the neck conjointly. 



The Brachial Plexus (Plate 3) is composed of the nerves for the 

 supply of the fore limb. It is formed by the inferior primary branches 

 of the last three cervical (6th, 7th, and 8th) and first two dorsal nerves. 

 These, however, do not enter into it in equal proportions. The 6th 

 cervical sends only a very slender branch to it, while the 7th and 

 8th, after detaching a communicating filament to the sympathetic, 

 are wholly expended in it. The 1st dorsal is, with the exception of a 

 similar communicating filament and a slender intercostal branch, also 

 entirely expended in it, but the 2nd dorsal gives off, besides the usual 

 communicating branch, a considerable intercostal nerve before joining 

 the plexus. 



These roots of the plexus converge towards each other, and come out 

 as a flat fasciculus between the upper and lower portions of the scalenus. 

 In descending to this point the dorsal roots of the plexus turn round 

 the anterior border of the first rib, leaving on it a smooth impression 

 near its upper end. The several roots anastomose in an intricate 

 fashion, contributing to the formation of the various branches of the 

 plexus in proportions that the student will not be able to trace 

 accurately in the course of an ordinary dissection. 



The manner in which the several roots of the plexus comport themselves is liable to 

 slight variation, but the following is probably as common as any other : — 



I. The root from the 6th cervical nerve is a slender branch detached from the division 

 which that nerve sends to aid in the formation of the phrenic. Passing obliquely back- 

 wards on the scalenus muscle, it resolves itself into three divisions — or rather its fibres 

 are traceable in three groups, viz., — 1. To the suprascapular nerve ; 2. to the anterior 

 root of the median ; 3. to join branches from all the other roots of the plexus in forming 

 a broad, flat fasciculus from which arise the subscapular, circumflex, and musculo-spiral 

 nerves. 



II. The root from the 7th cervical nerve gives a branch to the nerve for the serratus 

 magnuB, and then divides its flbres in three directions, viz., — 1. To the above-mentioned 

 fasciculus giving oft the subscapular, circumflex, and musculo-spiral nerves ; 2. to the 

 suprascapular nerve ; 3. to the phrenic, anterior root of the median, and nerve for the 

 anterior deep pectoral muscle. 



