Flexor digiti minimi brevis flexes the little finger at the metacarpophalangeal joint.
The flexor digiti minimi brevis (FDMB) is one of the three intrinsic hypothenar muscles of the hand. It functions to flex the little finger at the metacarpophalangeal joint and contributes to the bulk and mobility of the ulnar side of the palm. Despite its name, there is no "longus" equivalent in the human hand.
The FDMB is situated in the hypothenar compartment of the palm, lying just lateral to the abductor digiti minimi and superficial to the opponens digiti minimi. It extends from the hamate bone to the proximal phalanx of the fifth digit.
The flexor digiti minimi brevis performs the following actions:
Supplied by the deep branch of the ulnar nerve (C8–T1).
The FDMB lies medial to the flexor tendons of the fingers and lateral to the abductor digiti minimi. Deep to it is the opponens digiti minimi. The ulnar nerve and artery pass deep to the hypothenar muscles as they enter the palm.
The FDMB contributes to the hypothenar bulge, becoming palpable during flexion of the little finger against resistance. It lies slightly lateral to the abductor digiti minimi.
The muscle develops from the ulnar side of the hand’s mesenchymal muscle mass. It is homologous with the flexor pollicis brevis of the thenar compartment.
In lower primates and quadrupeds, the hypothenar muscles are generally less developed due to limited use of the fifth digit. In humans, the FDMB is part of a specialized muscle group supporting fine motor control and dexterous grip on the ulnar side of the hand.