There are four dorsal interossei muscles. The most superficial of all dorsal muscles, these can be palpated on the dorsum of the hand. In addition to their actions of abduction (dorsal interossei) and adduction (palmar interossei) of the fingers, the interossei also assist the lumbricals in flexion at the MCP joints and extension at the IP joints. They can be divided into two groups – dorsal and palmar.

The interossei muscles are located between the metacarpal bones of the hand. Actions: Flexes the metacarpophalangeal joint of the little finger.Attachments: Originates from the hook of hamate and adjacent flexor retinaculum, and inserts into the base of the proximal phalanx of the little finger.The flexor digiti minimi brevis lies laterally to the abductor digiti minimi in the hand. It attaches to the base of the proximal phalanx of the little finger.

Attachments: Originates from the pisiform and the tendon of the flexor carpi ulnaris.The abductor digiti minimi is the most superficial of the hypothenar muscle group. Actions: It rotates the metacarpal of the little finger towards the palm, producing opposition.Attachments: Originates from the hook of hamate and associated flexor retinaculum, inserts into the medial margin of metacarpal V.The opponens digit minimi lies deep to the other hypothenar muscles. The ulnar nerve innervates the muscles of the hypothenar eminence. These muscles are similar to the thenar muscles in both name and organisation. The hypothenar muscles form the hypothenar eminence – a muscular protrusion on the medial side of the palm, at the base of the little finger. The deep head is innervated by the deep branch of the ulnar nerve. Innervation: Median nerve (recurrent branch).Actions: Flexes the metacarpophalangeal joint of the thumb.Attaches to the base of the proximal phalanx of the thumb. Attachments: Originates from the tubercle of the trapezium and from the associated flexor retinaculum.It is described as having a superficial and deep part – although the deep component is variable in size. The flexor pollicis brevis forms the medial aspect of the thenar eminence. Attaches to lateral side of proximal phalanx of the thumb. Attachments: Originates from the tubercles of the scaphoid and trapezium, and from the associated flexor retinaculum.The abductor pollicis brevis forms the anterolateral aspect of the thenar eminence, overlying the opponens pollicis. Actions: Opposes the thumb, by medially rotating and flexing the metacarpal on the trapezium.It inserts onto the lateral margin of the first metacarpal. Attachments: Originates from the tubercle of the trapezium and the associated flexor retinaculum.The opponens pollicis is the largest of the thenar muscles, and lies underneath the other two. The median nerve innervates all the thenar muscles. They are responsible for the fine movements of the thumb. The muscle bellies produce a bulge, known as the thenar eminence. The thenar muscles are three short muscles located at the base of the thumb.

Middle finger female drawing