3i6 A MANUAL OF ANATOMY 



which is of small size, derives its fibres from the fifth and sixth 

 cervical. It is situated high up on the posterior wall of the axilla, 

 and after a short course it enters the upper part of the subscapu- 

 laris. The middle or long subscapular nerve derives its fibres 

 chiefly from the seventh cervical, but to a certain extent also from 

 the sixth and eighth. It descends along with the subscapular 

 artery to the latissimus dorsi, which it supplies. The lower sub- 

 scapular nerve derives its fibres from the fifth and sixth cervical. 

 On approaching the lower border of the subscapularis it breaks 

 up into branches, some of which enter the lower part of that muscle, 

 whilst others pass to the teres major. 



The circumflex nerve derives its fibres from the fifth and sixth 

 cervical. For a short distance it lies behind the axillary artery, 

 resting on the subscapularis, but, at the lower border of that muscle, 

 it passes backwards through the quadrangular muscular space in 

 company with the posterior circumflex artery. In doing so it 

 furnishes an articular branch to the shoulder- joint, and then breaks 

 up into an upper or anterior and a lower or posterior division. 

 The upper or anterior division accompanies the posterior circumflex 

 artery, and divides into a number of branches which enter the 

 deep surface of the deltoid over its anterior part. Some of the 

 branches, piercing the muscle, supply the integument over about its 

 middle third. The loiver or posterior division gives branches to the 

 posterior part of the deltoid, a branch to the teres minor, and a 

 cutaneous branch, which latter turns round the posterior border of 

 the deltoid to be distributed to the integument over its lower third. 

 The nerve to the teres minor presents a small reddish swelling, 

 which has the appearance of a ganglion, but is really a fibrous 

 thickening. 



In connection with the distribution of the circumflex nerve 

 Hilton's law may be here stated as follows : a nerve trunk, supply- 

 ing a given joint, also supplies the muscles moving that joint, and 

 the integument covering their insertions. For example, the circum- 

 flex nerve supplies the shoulder- joint, the deltoid, and the integu- 

 ment covering its insertion. This law, however, is not universally 

 applicable. 



The musculo-spiral nerve is the largest of all the branches of the 

 plexus, and is the continuation of the posterior cord. It derives its 

 fibres from the last four cervical nerves, and sometimes from the first 

 thoracic. It descends behind the third part of the axillary artery, 

 resting upon the subscapularis, latissimus dorsi, and teres major. 

 Whilst in the axillary space it gives off muscular and cutaneous 

 branches. The muscular branches are destined for the long and 

 inner heads of the triceps, those for the long head entering it 

 high up, whilst those for the inner head enter it at different levels. 

 One of the latter, which is remarkable for its length, descends 

 in company with the ulnar nerve to enter the inner head low 

 down, this branch being known as the ulnar collateral nerve 

 (Krause). The internal cutaneous branch usually arises in common 



