SPINAL NERVES. 



and anterior and external to the first rib, and 

 there divides into its terminal branches. In 

 the neck, the plexus is situated superior, pos- 

 terior, and external to the artery ; but as the 

 trunks gradually converge towards the axilla, 

 and the terminal branches again diverge, the 

 artery comes to be bounded by some inter- 

 nally, by others externally. The plexus is 

 broad above, where it represents the base of 

 a triangle, and narrow below at its termina- 

 tion at the upper part of the axilla. 



The different branches of the plexus may 

 be divided into those given off above, and 

 those below the clavicle : the former, for 

 the levator anguli scapula, subclavius, rhom- 

 boid, and serratus magnus; the latter, for the 

 upper extremity and its muscles. 



Supra-clavicular 



Infra- clavicular 



Muscular, supra-scapular. 



Subscapular. 



Internal cutaneous. 



External cutaneous. 



Median. 



Ulnar. 



Musculo-spiral. 

 _ Circumflex. 

 Of the muscular branches. The nerve for 

 the rhomboidens takes its origin from the an- 

 terior branch of the fifth cervical, immediately 

 after it has quitted the intervertebral foramen ; 

 but is frequently given off from the cervical 

 plexus : it is, consequently, deeply seated. 

 It either perforates the scalenus porticus 

 or winds round it, to get between it and the 

 levator anguli scapulae ; continues along the 

 costal surface of the latter muscle, and then 

 passes to the same surface of the rhomboi- 

 deus, as far as its lower part, frequently sup- 

 plying, in its course, the levator anguli sca- 

 pulae, which, in many cases, however, receives 

 filaments from a distinct nerve arising above 

 it, and taking a similar course. 



The nerve to the serratus magnus (external 

 respiratory, posterior thoracic), situate at the 

 posterior and upper part of the plexus, arises 

 from it by two delicate roots, which come off 

 from the lower edge of the fifth and sixth 

 cervical, immediately after they have passed 

 the intervertebral foramina. It receives, 

 sometimes, a twig from the seventh. It is 

 directed downwards and outwards, and reaches 

 the thorax between the subscapularis and ser- 

 ratus magnus, passing behind the axillary 

 vessels. It passes along this muscle inferior, 

 to the long thoracic artery, and terminates in 

 its lower part, by numerous filaments. 



The nerve for the subclavius is very small, 

 but always present, and is given off from the 

 anterior part of the united trunk of the fifth 

 and sixth cervical. It passes down anterior 

 to the subclavian artery, and enters the mid- 

 dle of the muscle. 



The remainder of the muscular branches 

 are very small, and come off from the lower 

 and anterior part of the plexus, being princi- 

 pally derived from the seventh cervical : some 

 pass behind, and others, in front of the ax- 

 illary artery, enter the axilla, and are distri- 

 buted to the posterior surfaces of the pecto- 

 ralis major and minor. They are known 



under the collective name of anterior or short 

 thoracic. 



The supra-scapular nerve, larger than the 

 long thoracic, issues from the upper and back 

 part of the plexus, from the united root of 

 the fifth and sixth cervical at their angle of 

 union. It Is directed downwards, outwards, 

 and backwards in company with the supra- 

 scapular vessels, passes behind the trapezius 

 and coracoid process to the notch in the upper 

 edge of the scapula, beneath the ligament 

 which converts this notch into a foramen, 

 and which separates it from the supra-scapular 

 vessels. Having reached the supra-spinal 

 fossa, and supplied the supra-spinatus muscle, 

 it winds along the concave external border of 

 the spine, and reaches the infra-spinal fossa, 

 supplying the infra-spinatus. From the in- 

 ferior filaments one or two twigs can be traced 

 to the teres minor. 



The subscapular nerves are intended for the 

 latissimus dorsi, teres major, and subscapularis. 

 That for the first muscle is the largest and 

 longest. It arises from the plexus above, 

 and internal to the circumflex nerve, passes 

 down in the axilla between the subscapularis 

 and serratus magnus, parallel, but posterior 

 to the long thoracic, and terminates by reach- 

 ing the lower border of the latissimus dorsi, 

 where it enters its substance. It gives off 

 occasionally in its course the branch from the 

 teres major, which usually, however, arises 

 from the plexus below it. This nerve passes 

 downwards and outwards at the subscapularis, 

 and enters the anterior surface of the teres 

 major. 



The nerves for the subscapularis are : a small 

 one, generally constant as to its origin arising 

 high up from the same source of origin as 

 the circumflex, passing behind the axillary 

 artery to the upper part of the superficial 

 surface of the subscapularis ; the other larger, 

 and frequently derived from the circumflex, 

 to be distributed to the middle of the muscle. 



The internal cutaneous, the smallest of the 

 terminal branches of the brachial plexus, and 

 situated most internally, takes its origin princi- 

 pally from the last cervical and first dorsal. It 

 descends, covered in by the brachial aponeuro- 

 sis, along the inner aspect of the arm, between 

 the median and the ulnar, and concealed above 

 by the axillary artery. Deeply seated in the 

 axilla, in leaving this cavity it inclines slightly 

 forwards and outwards in company with, but 

 anterior to, the basilic vein ; and at a variable 

 distance from the elbow joint, generally a 

 little below the middle of the arm, divides 

 into external and internal cutaneous foanches: 

 both of which perforate the fascia. In this 

 part of its course the internal cutaneous gives 

 off in the axilla a small cutaneous filament, 

 which, having communicated with the second 

 or third intercostal nerve, perforates the fascia, 

 and supplies the skin on the inner part of the 

 arm as far as the internal condyle. 



The external terminal branch, the continua- 

 tion of the trunk in the arm, and the larger 

 of the two, divides into two or three twigs, 

 which pass either in front or behind the 



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