MUSCULO-SPIEAL NEEVE PAEALYSIS. 239 



the abductor pollicis, the flexor ossis metacarpi pollicis and the 

 flexor brevis pollicis (superficial head). 



The rest of the nerve is supplied to the two radial lumbricales, 

 and to the skin on the palmar aspect of the thumb, index, middle 

 and the radial half of the ring finger. The terminal filaments 

 of these cutaneous branches also pass round on to the dorsal 

 aspect of the thumb and supply the bed of the nail, and to the 

 dorsal aspect of the index, middle and the radial half of the ring 

 finger, to supply sensation as high as the middle of the second 

 phalanx, about the level beyond which cutaneous hairs cease to 

 be found. 



It will thus be seen that in division of the median nerve close 

 above the wrist there will be loss of power of abducting the thumb 

 and of directly flexing its metacarpal bone and proximal phalanx ; 

 also loss of sensation on the whole of the palmar aspect of the 

 thumb, index, middle, and radial half of the ring finger, and 

 over the dorsal aspect of the same, in the case of the thumb 

 extending upwards as far as the middle of the terminal phalanx, 

 and in the case of the other digits as high as the middle of the 

 second phalanges. 



The musculo-spiral nerve is derived from the posterior 

 cord of the brachial plexus and lies at first behind the third 

 portion of the axillary and the commencement of the brachial 

 artery. It then winds round the inner side of the humerus to 

 reach the musculo-spiral groove on the posterior aspect of the 

 bone, between the external and internal heads of the triceps 

 muscle, to appear on the outer side of the arm above the elbow 

 between the brachio-radialis and the brachialis anticus. 



During this course it supplies the following muscles : The 

 three heads of the triceps, the anconeus, brachio-radialis, extensor 

 carpi radialis longior, and a small portion of the brachialis 

 anticus, in addition to giving one internal and two external 

 cutaneous branches. Finally, it divides into its two terminal 

 branches, the radial and the posterior interosseous. 



The radial nerve is purely cutaneous and is distributed to the 

 dorsal aspect of the thumb, as low down as the bed of the nail, 



