The structure indicated is the abductor digiti minimi muscle of the hand.

The abductor digiti minimi muscle is one of the intrinsic muscles of the hand that belongs to the hypothenar group.

The hypothenar group of intrinsic hand muscles consist of three muscles:

1. Abductor digiti minimi
2. Opponens digiti minimi
3. Flexor digit minimi brevis

All the intrinsic muscles of the hand, except the thenar muscles and the lateral two lumbrical muscles are innervated by the deep branch of the ulnar nerve. The thenar muscles and the lateral two lumbrical muscles are innervated by the median nerve.  A useful mnemonic for remembering this is MEATLOAF. “MEAT” refers to the Median nerve, and LOAF refers to the muscles which it innervates: Lateral two lumbricals, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis.

Origin: Pisiform

Insertion: Medial base of proximal phalanx of little finger

Innervation: Deep branch of ulnar nerve

Action: Abducts little finger

Learn all about the anatomy of the muscles of the hand in this tutorial.