| OCR Text |
Show 708 MR. F. G. PARSONS O N T H E [June 16 of the atlas from which communicating branches are given off. From the 3rd cervical a single large nerve passes to the auricle and occiput, which evidently corresponds to the small occipital and great auricular. From the 3rd also come two superficial cervical nerves, which supply the skin over the anterior and posterior triangles of the neck respectively. The 4th cervical nerve communicates with the upper part of the 5th, and from the junction come off descending cutaneous branches to the skin of the arm and shoulder. From the deep part of the plexus branches are given off to the surrounding muscles, a small communicating spinal accessory coming from the 4th. The arrangement of the Brachial Plexus corresponds very closely with that of M a n ; it is chiefly remarkable for the fact that the subscapularis is supplied by three separate twigs, one of which is derived from the suprascapular nerve and the other two from the posterior cord. There is no distinct musculo-cutaneous nerve, the coraco-brachialis, biceps, and brachialis anticus being supplied by tbe outer head of the median. The suprascapular comes off after the junction of the 5th and 6th cervicals. The external anterior thoracic is given off from the outer cord after tbe junction of the 7th cervical, but has no communication with the internal anterior thoracic. The outer head of the median is, as in Man, derived from the 5th, 6th, and 7th; it is not joined by the inner head, which comes from the 8th cervical and 1st dorsal, until it reaches the middle of the arm. The trunk formed by the union of the two heads passes through the supracondylar foramen and just below the elbow divides into two branches, the outer of which corresponds in its distribution to the human radial nerve, that is to say it supplies the three and a half outer fingers on their dorsal surfaces ; in its course down the forearm it lies superficial to all the muscles. The inner of the two branches gives off twigs to the flexor muscles of the forearm aud accompanies the median artery to the hand, passing deep to the pronator radii teres, palmaris longus, and flexor carpi radialis. In the hand it supplies the thenar muscles as well as the skin of the outer three and a half fingers on their palmar surfaces. There is no distinct anterior interosseous branch. The ulnar nerve separates from the inner head of the median just above the middle of the arm ; it at once gives off two internal cutaneous branches for the inner side of the forearm and then passes deep to the epitrochleo-anconeus, which it supplies. Immediately after this it gives off a branch to the flexor carpi ulnaris, but none to tbe flexor profundus digitorum, and passes down the forearm under cover of the flexor carpi ulnaris to the radial side of the pisiform bone, giving off, at the junction of the middle and lower thirds of the forearm, a dorsal cutaneous branch, which supplies the back of the inner one and a half fingers. At the pisiform the main stem of the ulnar divides into superficial and deep branches, the former supplying the skin of the ulnar one and a half fingers on their palmar surfaces, the latter passing between |
