392 NERVOUS SYSTEM. 



second digit. The second passes along the contiguous sides 

 of the second and third digits and supplies their integument. 

 The third passes along the contiguous sides of the third and 

 fourth digits to their integument. Each sends twigs into the 

 trilobed pad in the palm, so that there are thus seven terminal 

 branches in the palm. From these, branches (probably) pass 

 to the three radial Mm. lumbricales. 



lo. N. radialis. — The radial (or musculospiral) nerve is 

 formed by the junction of branches from the seventh and eighth 

 cervical and first thoracic nerves. It immediately sends 

 branches to the epitrochlearis, long head of the triceps, and 

 long and intermediate portions of the medial head of the triceps. 

 It then passes between the long and intermediate portions of the 

 medial head of the triceps, following the profunda brachii artery, 

 and curves about the humerus to its cranial side. It supplies 

 there the lateral head of the triceps and the anconeus, and, 

 lying on the brachialis muscle, divides into a superficial and a 

 deep branch. The superficial branch is the superficial radial 

 nerve (Fig. 130,^); the deep one forms the dorsal (or pos- 

 terior) interosseous nerve. The former is sensory and the latter 

 motor. 



The superficial radial nerve (Fig. 130, g, page 319) 

 becomes cutaneous at the junction of the second and third thirds 

 of the upper arm, where it emerges from between the lateral 

 head of the triceps and the brachialis muscle. It then follows 

 the course of the vena cephalica (r) to the wrist and follows the 

 dorsal tributary of the same vein onto the dorsum of the hand. 

 It supplies the integument of the distal part of the ventral sur- 

 face of the upper arm and that along the forearm. On the 

 hand it is distributed to the dorsal surface in the same manner 

 as the median nerve on the ventral surface, i.e. to the integu- 

 ment of the thumb on both sides and to that of the medial side 

 of the second digit; to that of the contiguous sides of the 

 second and third digits and of the contiguous sides of the third 

 and fourth digits. There are thus seven terminal branches, 

 one for each of these regions. 



The dorsal interosseous nerve follows the brachialis muscle 

 and passes onto the forearm between it and the extensor carpi 



