In human anatomy, the abductor digiti minimi (abductor minimi digiti, abductor digiti quinti, ADM) is a skeletal muscle situated on the ulnar border of the palm of the hand. It forms the ulnar border of the palm and its spindle-like shape defines the hypothenar eminence of the palm together with the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

, and fat surrounding it. Its main function is to pull the little finger away from the other fingers (i.e.

abduction Abduction may refer to: Media Film and television * "Abduction" (''The Outer Limits''), a 2001 television episode * " Abduction" (''Death Note'') a Japanese animation television series * " Abductions" (''Totally Spies!''), a 2002 episode of an ...

Structure

The abductor digiti minimi arises from the pisiform bone, the pisohamate ligament, and the flexor retinaculum. Its distal tendon ends in three slips that are inserted into the ulnopalmar margin of the proximal phalanx, the palmar plate of the

metacarpophalangeal joint The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow ...

, and the sesamoid bone when present. Some fibers insert into the finger's dorsal aponeurosis, which is why the muscle acts similar to a dorsal interosseus muscle. Additionally, the ulnar-most portion of the tendon inserts into the little finger's digital cord, and the muscle thus forms part of a structure that flexes the metacarpophalangeal joint and extends the interphalangeal joints.

Innervation

It is innervated by the deep branch of the ulnar nerve ( C8– T1).

Development

The abductor digit minimi develops at an early stage from an ulnar muscle primordium of the superficial layer of the original undifferentiated mesenchyme of the hand, together with the

flexor digitorum superficialis Flexor digitorum superficialis (''flexor digitorum sublimis'') is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints. It is in the anterior compartment of the forearm. It is sometimes considered to be the deepest p ...

(medial primordia) and the

abductor pollicis brevis The abductor pollicis brevis is a muscle in the hand that functions as an abductor of the thumb. Structure The abductor pollicis brevis is a flat, thin muscle located just under the skin. It is a thenar muscle, and therefore contributes to the ...

(radial). In contrast, the remaining hypothenar muscles are derived from the deep layer at a later stage.

Variation

In rare cases accessory fascicles of the abductor digiti minimi have been found arising from the antebrachial fascia, the

radius In classical geometry, a radius (plural, : radii) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', ...

, and the ulna. The abductor digiti minimi is the most variable hypothenar muscle, and might be joined by accessory slips from the tendon of the flexor carpi ulnaris, the flexor retinaculum, the fascia of the distal forearm, or the tendon of the palmaris longus. Occasionally, the muscle is partially inserted onto the fifth metacarpal bone. In case of

polydactyly Polydactyly or polydactylism (), also known as hyperdactyly, is an anomaly in humans and animals resulting in supernumerary fingers and/or toes. Polydactyly is the opposite of oligodactyly (fewer fingers or toes). Signs and symptoms In hum ...

it may insert to the sixth finger instead, if there is one.

Function

It is an abductor of the little finger at the

.Origin, insertion and nerve supply of the muscle
at Loyola University Chicago Stritch School of Medicine It is also possible that the muscle contributes to extension of the middle phalanx of the little finger through its connection to finger's extensor mechanism. It plays an important role when the hand is grasping large objects with outspread fingers.

Etymology

The name is derived from the Latin -''ab'' "away from"; ''ducere'' "to draw"; ''digitus'', "digit"; and ''minimum'', smallest; or ''quintus'', "fifth", meaning "abductor of the smallest or fifth finger".

Additional images

File:Gray422.png, Transverse section across the wrist and digits. File:Hand dissection 6.jpg, Abductor digiti minimi muscle File:Slide1MAI.JPG, Muscles of hand. Cross section.

References

{{Authority control Muscles of the upper limb Abductors (muscles)