human anatomy Human anatomy (gr. ἀνατομία, "dissection", from ἀνά, "up", and τέμνειν, "cut") is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross ...

, the abductor digiti minimi (abductor minimi digiti, abductor digiti quinti, ADM) is a

skeletal muscle Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the somatic nervous system, voluntary muscular system and typically are a ...

situated on the

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

r border of the palm of the

hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the Koala#Characteristics, koala (which has two thumb#O ...

. It forms the ulnar border of the

palm Palm most commonly refers to: * Palm of the hand, the central region of the front of the hand * Palm plants, of family Arecaceae ** List of Arecaceae genera **Palm oil * Several other plants known as "palm" Palm or Palms may also refer to: Music ...

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, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesod ...

, and

fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers specif ...

surrounding it. Its main function is to pull the little finger away from the other fingers (i.e. abduction).

Structure

The abductor digiti minimi arises from the

pisiform bone The pisiform bone ( or ), also spelled pisiforme (from the Latin ''pisiformis'', pea-shaped), is a small knobbly, sesamoid bone that is found in the wrist. It forms the ulnar border of the carpal tunnel. Structure The pisiform is a sesamoid 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 In anatomy, a sesamoid bone () is a bone embedded within a tendon or a muscle. Its name is derived from the Greek word for 'sesame seed', indicating the small size of most sesamoids. Often, these bones form in response to strain, or can be presen ...

when present. Some fibers insert into the finger's dorsal

aponeurosis An aponeurosis (; : aponeuroses) is a flattened tendon by which muscle attaches to bone or fascia. Aponeuroses exhibit an ordered arrangement of collagen fibres, thus attaining high tensile strength in a particular direction while being vulnerable ...

, 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 A primordium (; : primordia; synonym: anlage), in embryology, is an Organ (anatomy), organ or tissue in its earliest recognizable stage of development. Cell (biology), Cells of the primordium are called primordial cells. A primordium is the simp ...

of the superficial layer of the original undifferentiated

mesenchyme Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood, or bone. The interactions between mesenchyme and epithelium help to form nearly ever ...

of the hand, together with the flexor digitorum superficialis (medial primordia) and the abductor pollicis brevis (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 (: radii or radiuses) 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 radius of a regular polygon is th ...

, and the

. 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 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:Carpal-Tunnel.svg, 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)