THE RADIAL NERVE 797 



in the middlf tliird of the forearm, erossing the pronator radii teres. It then i)arts 

 company Avith the artery by bending Ijaekwards on the deep surface of the tendon 

 of the sui)inator longus. It pierces the deep fascia in the lower third of the fore- 

 arm and is directed towards the back of the wrist, where it divides into its terminal 

 ^tranches. One of these, the })almar cutaneous of the radial nerve, sup])lies the 

 outer part of the thenar eminence; two others supply the dorsum of the thumb, a 

 fourth branch runs along the radial side of the index finger, a fifth divides to 

 supi)ly the adjacent side of the index and middh? fingers, and a sixth branch com- 

 municates with the dorsal branch of the ulnar nerve to sup])ly the adjacent side of 

 the middle and ring fingers. 



Nerve-supply of the dorsal integument to the hand. — It will be seen, by the foregoing 

 description of tiie radial and ulnar ncirves, that the tliuiub, index, and half the middle finger are 

 supplied by the nulial ; the little and half the ring finger by the ulnar ; and the adjacent sides 

 of the ring and middle fingers by both radial and ulnar nerves. The distance to which these 

 nerves extend on the digits is somewliat variable, but the following is the average condition: — The 

 radial nerve extends to the base of the thumb nail, to the distal interphalangeal joint of the index, 

 and not (juite to the proximal interphalangeal joint of the middle finger, and sends a fine twig 

 in some ca.ses to the skin covering the metaphalangeal articulation of the ring finger. The ulnar 

 nerve extends to the nail of the little finger, to the distal interphalangeal joint of the ring, and 

 in some eases to the integument covering the proximal interphalangeal joint of the middle, and 

 the metacarpo-phalangeal articulation of the index finger. The distal paits of the dorsum of the 

 fingei-s are supplied by twigs fr(jm the palmar collateral branches of the median and ulnar nerves, 

 almost tlu^ whole of the middle finger being supi)lied in this way, and the other digits to a less 

 degree. The matrix of the thumb nail is supplied by twigs from the jjalmar branches of the median. 

 A considerable part of the dorsum of the hand is usually supi)lied by twigs from both the radial 

 and the ulnar nerves, as these nerves overlap one another in their distribution (fig. 459). 

 Occasionally two other nerves, the musculo-cutaneous and the l(jwer external cutaneous branch 

 of the museulo-spiral, take part in the supply of the back of the hand. 



Table Showing Relation of Cervical and Dorsal Nerves to Branches or 



Brachial Plexus 



Nerve Roots. Kerves. 



- Q J Nerve to rhomboids 



'■ ,, subclavius 



f Suprascapular 

 I Nerve to subclavius 



5 and 6 C Upper subscapular 



Lower , , 



Circumflex 

 ( Posterior thoracic 



5, 6. and 7 C \ External anterior thoracic 



^ Musculo-cutaneous 



5, 6, 7, and 8 C Musculo-spiral 



6, 7, 8C., and 1 D Median 



7 and 8 C Middle subscapular 



r Internal anterior thoracic 



8 C. and ID J Ulnar 



i Internal cutaneous 



ID Lesser internal cutaneous 



