584 



THE EEACHIAL PLEXUS. 



instances in which it received a fourth branch or root from the eighth cervical. 

 Its highest root from the fifth cervical nerve is frequently united at its origia 

 ■with the nerve to the rhomboids. 



BKANCHES BELOW THE CLAVICLE. 



The several nerves now to be described are derived from the three 

 great cords of the plexus in the following order. 



From the upper or outer cord, — the external of the two anterior 

 thoracic nerves, the musculo-cutaneous, and the outer root of the 

 median 



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

 the nerve of Wrisberg, the internal cutaneous, the ulnar, and the inner 

 root of the median. 



From the posterior cora, — the subscapular nerves, the circumflex, and 

 the musculo-spiral. 



If the fasciculi of which the principal nerves are composed be follovs'ed 

 through the plexus, they may be traced to those of the spinal nerves which in 

 the subjoined table are named along with each trunk. The higher numbers 

 refer to the cervical nerves, the unit to the dorsal nerve : — 



Subscapular from 

 Cu'cumflex 

 Musculo-spiral . 

 External cutaneous 

 Median 



.8. 



. i 0.6.7 



. 5.6.7. 



. .5.6.7.8.1. 



Ulnar . . . . 8.1. or 

 Internal cutaneous •} a-i 



Small internal cutaneous )' ' 



{ outer .5.0.7. 



\ inner 8.1. 



■.8.1. 



Anterior thoracic 



Anterior thoracic nerves. — The anterior thoracic nerves, two in 

 number, supply the pectoral muscles. 



The external, or more superficial branch, arising from the outer cord, 

 crosses inwards over the axillary artery, and terminates in the great 

 pectoral muscle. 



The internal, or deeper branch, springing from the inner cord, comes 

 forwards between the axillary artery and vein to the small pectoral 

 muscle, and is joined by a branch from the external. This nerve pre- 

 sents a plexiform division beneath the small pectoral muscle, and sup- 

 plies branches to it and the larger pectoral muscle. The two nerves 

 are connected by a filament which forms a loop over the artery, at the 

 inner side. 



Subscapular nerves. — These nerves, three in number, take origin 

 from the posterior cord of the plexus. 



The vppcr nerve, the smallest of the subscapular nerves, penetrates 

 the upper part of the subscapular muscle. The middle nerve gives a 

 branch to the subscapularis at its axillary border, and ends in the teres 

 major muscle. There is sometimes a distinct nerve for the last-named 

 muscle. 



The tonrj sadsrajwtar nerve, the largest of the three, runs along the 

 lower border of the subscapular muscle to the latissimus dorsi, to which 

 it is distributed. 



Circumflex nerve. — The circumflex nerve gives both muscular and 

 cutaneous nerves to the shoulder. Springing from the posterior cord, 

 this nerve is at first placed behind the axillary artery, but at the lower 

 border of the subscapular muscle it is inclined backwards with the 

 posterior circumflex artery, in the space between the scapula and teres 

 major muscle above the long head of the triceps, and separates into an 



