5U 



NERVES OF THE UPPER LIMB. 



Posterior interosseous nerve. — This nerve, the larger of the two 

 divisions of the musculo-spiral nerve, winds to tlie back of the forearm 

 through the fibres of the supinator brevis muscle, and is prolonged 

 between the deep and superficial layers of the extensor muscles to the 

 interosseous membrane, which it approaches about the middle of the 

 forearm. 



Fig. 3G4. Fig. 364. — View op the Radial side of the Forearm, 



SHOWING THE FINAL DISTRIBUTION OF THE MuSCULC- 



li{< •!JllJ)»\ Spiral Nerve (after Hirschfeld and Leveille). 5 



The supinator longus, and extensores carpi radiales longior 

 and brevior have been divided, and their upper parts re- 

 moved ; the extensor communis digitorum is pulled back- 

 wards by a hook, and the supinator brevis has been par- 

 tially dissected to show the posterior interosseous nerve 

 passing through it. 



1, placed upon the tendon of the biceiw muscle, points 

 to the inusculo-cutaneous nerve ; 1', near the wrist, the 

 lower part of this nerve and its plexus of union with the 

 radial nerve ; 2, trunk of the musculo-spiral nerve emerg- 

 ing from between the brachialis anticus, on which the 

 number is placed, and the supinator longus muscle ; 2', 

 its muscular twigs to the long supinator and long radial 

 extensor of the carpus ; 2", the posterior interosseous nerve 

 passing through the substance of the supinator brevis ; 3, 

 placed upon the cut lower portion of the supinator longus, 

 and lower down the radial nerve ; 4, the external collateral 

 nerve of the thumb ; 5, the common collateral of the fore- 

 finger and thumb ; 6, the common collateral of the fore-finger 

 and middle finger ; 7, the twig of \inion with the dorsal 

 branch of the ulnar nerve ; 8, pilaced upon the common ex- 

 tensor of the fingers, the muscular branches of the posterior 

 interosseous nerve to the long extensor muscles ; 9, upon 

 the extensor secundi internodii pollicis, the branches to the 

 short extensor muscles. 



Much diminished in size by the separation 

 of numerous branches for the muscles, the 

 nerve lies at the lower part of the forearm 

 beneath the extensor of the last phalanx of the 

 thumb and the tendons of the common extensor 

 of the fingers, and terminates on the back of 

 the carpus in a gangliform enlargement, from 

 mm ^\Jf which filaments are given to the adjoining 



ligaments and articulations. 



The hranchcx of the interosseous nerve enter the surrounding muscles, viz., the 

 extensor carpi radialis brevior and supinator brevis, the superficial layer of the 

 extensor muscles, except the anconeus, and the deep layer of the same muscles : — 

 that is to say, the nerve supplies the supinators, and the extensors of the carpus 

 and fingers, with the exception of the supinator longus and the extensor carpi 

 ladialis longior. 



Summary. — The m.usculo-spiral nerve distributes its branches to the 

 extensor muscles of the elbow-joint exclusively, with the exception of a 

 filament to the brachialis anticus, which, however, receives its principal 

 nerves from another source. Before separating into its two large 

 divisions, the nerve gives branches to two muscles of the forearm, viz., 

 the long supinator, and the long radial extensor of the carpus. The 



