CUTANEOUS NERVES
The superficial
branch of the radial nerve arises in the cubital fossa by the division
there of the radial nerve into deep and superficial branches (see Plates 3-13
and 3-16). The superficial branch, which is entirely cutaneous, courses through
the forearm under cover of the brachioradialis muscle and is accompanied by the
radial artery. At the distal third of the forearm, the superficial branch of
the radial nerve perforates the antebrachial fascia along the lateral border of
the forearm and divides into two branches.
The smaller lateral branch supplies
the skin of the radial side and eminence of the thumb and communicates with the
lateral antebrachial cutaneous nerve. The larger medial branch divides
into four dorsal digital nerves. The first dorsal digital nerve supplies the
ulnar side of the thumb; the second supplies the radial side of the index
finger; the third distributes to the adjoining sides of the index and middle
fingers; and the fourth supplies the adjacent sides of the middle and ring fingers.
There is usually an anastomosis on
the back of the hand between the superficial branch of the radial nerve and the
dorsal branch of the ulnar nerve, and there is some variability in the apparent
source of the last (more median) branch of either nerve. In some such cases,
the adjacent sides of the middle and ring fingers are in the territory of the
ulnar nerve. Dorsal digital nerves fail to reach the extremities of the digits.
They reach to the base of the nail of the thumb, to the distal interphalangeal
joint of the second digit, and not quite as far as the proximal interphalangeal
joints of the third and fourth digits. The distal areas of the dorsum of the
digits not supplied by the radial nerve receive branches from the stout palmar
digital branches of the median nerve.
The dorsal branch of the ulnar
nerve completes the cutaneous supply of the dorsum of the hand and digits
(see Plate 3-16). It arises about 5 cm above the wrist, passes
dorsalward from beneath the flexor carpi ulnaris tendon, and then pierces the
forearm fascia. At the ulnar border of the wrist, the nerve divides into three
dorsal digital branches.
The first branch courses along the
ulnar side of the dorsum of the hand and supplies the ulnar side of the little
finger as far as the root of the nail. The second branch divides at the cleft
between the fourth and fifth digits and supplies their adjacent sides. The
third branch may divide similarly; it may supply the adjacent sides of the
third and fourth digits, or it may simply anastomose with the fourth dorsal
digital branch of the superficial branch of the radial nerve. The dorsal
branches to the fourth digit usually extend only as far as the base of the
second phalanx, with the more distal parts of the fourth and fifth digits
supplied by palmar digital branches of the ulnar nerve.
The palmar branch of the ulnar
nerve arises about the middle of the forearm, descending under the
antebrachial fascia in front of the ulnar artery (see Plates 3-16 and 3-17). It perforates the fascia just above the
wrist and supplies the skin of the hypothenar eminence and the medial part of
the palm.
The palmar branch of the median
nerve arises just above the wrist (see Plates 3-16
and 3-17). It
perforates the palmar carpal ligament between the tendons of the palmaris
longus and flexor carpi radialis muscles and distributes to the skin of the
central depressed area of the palm and the medial part of the thenar
eminence.
