THE BRACHIAL PLEXUS. 



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thoracic nerve for the serratus magnus muscle, the suprascapular nerve, the nerve 

 to the subclavius, and sometimes a branch to join the phrenic nerve. 



The nerves given off below the clavicle are derived from the three great cords of 

 the plexus in the following manner : 



From the upper or outer cord, the external of the two anterior thoracic nerves, 

 the nerve to the coraco-brachialis, the musculo-cutaneous, aud the outer head of the 

 median. 



From the lower or inner cord, the inner of the two anterior thoracic nerves, 

 the nerve of Wrisberg or small internal cutaneous, the internal cutaneous, the ulnar, 

 and the inner head of the median. 



From the posterior cord, the three subscapular nerves, the circumflex, and the 

 musculo-spiral. 



The following table shows the spinal nerves from which the several offsets of the plexus 

 are commonly derived. 1 + signifies that the branch in question receives fibres from the 

 spinal nerve in whose column the sign is placed ; + ? signifies that there is most frequently 

 a root from that spinal nerve, but it may be wanting ; ? signifies that the corresponding root 

 is not unfrequently present, although exceptional. The rarer forms of variation are not taken 

 into account : 



A. BRANCHES ABOVE THE CLAVICLE. 



Small muscular branches. The branches for the scaleni and longus colli 

 muscles spring in an irregular manner from the lower cervical nerves close to their 

 place of emergence from the intervertebral foramina. 



Branch to the phrenic nerve. This small branch is, when present, an 

 offset from the fifth cervical nerve ; it usually joins the phrenic nerve on the 

 anterior scalenus muscle. 



1 See W. P. Herringham, 

 1886. 



The Minute Anatomy of the Brachial Plexus," Proc. Roy. Soc., xli, 



