Ulnar nerve

Ulnar Nerve
The ulnar nerve enters the palm anterior to the flexor
retinaculum alongside the lateral border of the pisiform
bone (Figs. 9.55 and 9.62). As it crosses the retinaculum, it
divides into a superficial and a deep terminal branch.
Superficial Branch of the Ulnar Nerve
The superficial branch of the ulnar nerve descends into
the palm, lying in the subcutaneous tissue between the
pisiform bone and the hook of the hamate (Figs. 9.55
and 9.62). The ulnar artery is on its lateral side. Here, the
nerve and artery may lie in a fibro-osseous tunnel, the
tunnel of Guyon, created by fibrous tissue derived from
the superficial part of the flexor retinaculum. The nerve
may be compressed at this site, giving rise to clinical signs
and symptoms.
The nerve gives off the following branches: a muscular
branch to the palmaris brevis and cutaneous branches to
the palmar aspect of the medial side of the little finger and
the adjacent sides of the little and ring fingers (Fig. 9.62).
It also supplies the distal half of the dorsal aspect of each
finger.
Deep Branch of the Ulnar Nerve
The deep branch of the ulnar nerve runs backward between
the abductor digiti minimi and the flexor digiti minimi
(Fig. 9.67). It pierces the opponens digiti minimi, winds
around the lower border of the hook of the hamate, and
passes laterally within the concavity of the deep palmar
arch. The nerve lies behind the long flexor tendons and in
front of the metacarpal bones and interosseous muscles.
It gives off muscular branches to the three muscles of the
hypothenar eminence, namely, the abductor digiti minimi,
the flexor digiti minimi, and the opponens digiti minimi.
It supplies all the palmar and dorsal interossei, the 3rd and
4th lumbrical muscles, and both heads of the adductor pollicis The palmar cutaneous branch of the ulnar nerve given
off in the front of the forearm crosses anterior to the flexor
retinaculum (Fig. 9.54) and supplies the skin over the
medial part of the palm (Fig. 9.38).