708 MB. F. G. PARSONS ON THE [June 10, 



of the atlas from wliich 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 ])osterior 

 triangles of the neck respectively. The 4th cervical nerve com- 

 municates 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 Ple»us corresponds very closely 

 with that of Man ; 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 museulo-cutaneous nerve, the 

 coraco-brachialis, biceps, and brachialis anticus being supplied by 

 the 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 the 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, 6lh, and 7th; it is not joined by the inner head, 

 which comes from the 8th cervical and 1st dorsiil, 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 

 tiexor muscles of the forearm and accompanies the median artery 

 to the hand, passing deep to the pronator radii teres, paluiaris 

 longus, and iiexor 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. Im- 

 mediately after this it gives off a branch to the flexor carpi ulnaris, 

 but none to the 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 



