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. 
10. 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 (c) 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 tle 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 
