CHAP, ix.] NERVOUS SYSTEM AND ORGANS OF SENSE. 279 



skin of the inner side of the arm. It pierces the fascia and becomes 

 cutaneous at about the middle of the inner side of the upper arm, 

 and is distributed to both the anterior and posterior surfaces of the 

 limb below the elbow. 



The external respiratory nerve of Sell, or posterior thoracic nerve, 

 at first traverses the scalenus muscle and then passes backwards 

 within (i.e., nearer the ribs than) the rest of the brachial plexus to 

 the side of the thorax, where it lies upon the serratus muscle, which 

 it supplies. 



The supra-scapular nerve passes between the trapezius muscle to 

 the dorsal surface of the scapula, and supplies the supra and infra- 

 spinatus muscles. 



The subscapular nerves pass to the inner side of the blade-bone, 

 and supply the subscapularis, teres major, and latissimus dorsi 

 muscles. 



.The musculo-cutaneous nerve descends obliquely through the 

 biceps and brachialis anticus muscles to the outer side of the fore- 

 limb. It supplies the muscles named as well as the coraco-brachialis, 

 and then proceeds to the skin of the outer side of the limb below the 

 elbow. 



The ULNAII nerve passes down on the inner side of the brachial 

 artery to the middle of the upper arm, and then turns backwards to 

 between the olecranon and inner condyle, where it is subcutaneous. 

 It then descends the lower arm (side by side with the ulnar 

 artery), supplying, in its course, the flexor profundus digitorum and 

 the flexor carpi ulnaris muscles. Arrived at about the lower third 

 of the ulnar artery, it bifurcates into a dorsal and a palmar branch. 

 The dorsal branch divides at the carpus into two branchlets, one of 

 which runs along the outside of the fifth digit, and the other (after 

 receiving a branch from the radial) subdivides and runs along the 

 inner side of the fifth, and the outer side of the fourth, digits. The 

 palmar branch passes within the pisiforme, and divides into branchlets, 

 which go to the muscles of the pollex and fifth digit and to the inter- 

 ossei; another passes along the outside of the fifth digit on its 

 palmar aspect ; another similarly supplies the contiguous sides of the 

 fourth and fifth digits, and sends a twig to the median nerve. 



The MEDIAN nerve descends and passes through the internal 

 condyioid foramen of the humerus. It then dips below the pronator 

 teres, and proceeds amidst the flexor muscles to the wrist ; 

 when beneath the annular ligament it divides into three branches. 

 On its way it supplies the pronators, the radial carpal flexors, and 

 the long flexors of the digits where not supplied by the ulnar 

 nerve. Of its three branches, the most internal goes to the pollex 

 and the adjacent palmar border of the index digit. The middle 

 branch descends into the second interosseous space, and supplies the 

 contiguous sides of the index and middle digits. The third branch 

 similarly supplies the adjacent sides of the third and fourth digits 

 on their palmar aspect. 



The CIRCUMFLEX (or axillary] nerve passes backwards at the 



