ORIGIN AND DISTRIBUTION OF THE NERVES. 137 



NERVES OF THE FORE EXTREMITY. 



The fore extremity receives its nerves from the axillary or 

 humeral plexus, and this plexus is formed by the union of 

 portions of the sixth and seventh cervical nerves, and a divis- 

 ion of the first dorsal nerve. 



The external thoracic nerves, six or seven in number, arise 

 from the humeral plexus, and are distributed to the pec- 

 toral, triceps, and other muscles ; they finally ramify into the 

 skin. 



The scapular nerves are called anterior, posterior, and sub- 

 scapular. The former sends its ultimate filaments to the 

 triceps. 



The posterior scapular nerve sends branches to the sub- 

 scapulars, triceps, teres minor, and shoulder joint, and ends 

 in the insertion of the levator humeri. 



The subscapular nerves run upward between the shoulder 

 and chest, and enter the subscapalaris. 



The spiral or external cutaneous nerve is furnished by the 

 axillary plexus ; arises behind the humeral artery, and passes 

 between the os humeri and the head of the triceps, through 

 the extensors, to the external flexors of the cannon. It gives 

 off several branches to the triceps, ramifies on the fore and 

 outward part of the knee, and sends branches to the heads of 

 the extensor muscles. 



The radial nerve descends with the humeral artery to the 

 inward side of the elbow joint, and runs along the back part 

 of the radius to the knee ; passing under the annular liga- 

 ment, it descends to the leg, and takes the name of the inter- 

 nal metacarpal nerve. It gives off numerous twigs to the 

 muscles, and finally becomes subcutaneous. 



The ulnar nerve originates from the humeral plexus. It 

 passes down the radius, under the annular ligament, to the 

 tendo perforans, and there becomes the external metacarpal 

 nerve. It gives off internal cutaneous and subcutaneous 

 branches, ramifies into cellular substance, penetrates the 

 heads of the flexors, and finally disperses its ramifications in 

 front of the leg. 

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