human anatomy The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis and the viability of the human body. It comprises a head ...

, the palmar or volar interossei (interossei volares in older literature) are three small, unipennate muscles in the hand that lie between the

metacarpal bones In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ar ...

and are attached to the

index Index (or its plural form indices) may refer to: Arts, entertainment, and media Fictional entities * Index (''A Certain Magical Index''), a character in the light novel series ''A Certain Magical Index'' * The Index, an item on a Halo megastru ...

, ring, and little fingers. They are smaller than the dorsal interossei of the hand.

Structure

All palmar interossei originate along the shaft of the metacarpal bone of the digit on which they act. They are inserted into the base of the proximal phalanx and the

extensor expansion An extensor expansion (extensor hood, dorsal expansion, dorsal hood, dorsal aponeurosis) is the special connective attachments by which the extensor tendons insert into the phalanges. These flattened tendons ( aponeurosis) of extensor muscles ...

of the extensor digitorum of the same digit.

Pollical palmar interosseous

The first palmar interosseous is located at the

thumb The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thu ...

's medial side. Passing between the first dorsal interosseous and the oblique head of adductor pollicis, it is inserted on the base of the thumb's proximal phalanx together with adductor pollicis. The "pollical" palmar interosseous muscle (PPIM), is present in more than 80% of individuals and was first described by . Its presence has been verified by numerous anatomists since, but others have either failed to mention it or considered it part of either adductor pollicis or

flexor pollicis brevis The flexor pollicis brevis is a muscle in the hand that flexes the thumb. It is one of three thenar muscles. It has both a superficial part and a deep part. Origin and insertion The muscle's superficial head arises from the distal edge of the f ...

. However, the deep head of the flexor pollicis brevis originates on the thumb's ulnar

sesamoid bone In anatomy, a sesamoid bone () is a bone embedded within a tendon or a muscle. Its name is derived from the Arabic word for 'sesame seed', indicating the small size of most sesamoids. Often, these bones form in response to strain, or can be prese ...

and the oblique portion of the adductor pollicis on several

carpal bones The carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, ...

, as well as the bases of the second and third

and not on the first metacarpal.

Central palmar interossei

The other three palmar interossei originate on the side of the metacarpal facing the hand's midline (ray of long finger); the second is attached to the medial side of the index finger; the third to the lateral side of the ring finger; and the fourth to the lateral side of the little finger. The tendons of these three muscles pass posterior to the deep transverse ligament before being inserted onto the extensor expansion.

Innervation

All of the interosseous muscles of the hand are innervated by the deep branch of the ulnar nerve.

Blood supply

The palmar interossei are supplied by the palmar metacarpal artery of the deep palmar arch.

Function

The palmar interosseous muscles ''adduct'' the fingers towards the middle finger. This is in contrast to the dorsal interossei, which ''abduct'' the fingers away from the middle finger. In addition (like dorsal interossei) they flex the finger at the metacarpo-phalangeal joint and extend the finger at the interphalangeal joint and thus assist the lumbricals. The palmar interossei, together with the dorsal interossei and the lumbricals, are active components of the finger's extensor mechanism.

Fibers Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate ...

from some of the interossei contribute directly to the extensor hoods that wrap around the proximal phalanges, while other fibers may contribute to the central

tendon A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...

and lateral bands of the mechanism. All three intrinsic groups of muscles pass palmar to the axis of the metacarpophalangeal joints, and therefore contribute to

flexion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

there. Extension at the interphalangeal joints cannot be produced by the extensor digitorum alone, but active contraction of one of the three aforementioned intrinsic groups will because of their direct contribution to the extensor mechanism.

Other animals

The pollical palmar interosseous muscle (PPIM) is absent in non-human

primate Primates are a diverse order (biology), order of mammals. They are divided into the Strepsirrhini, strepsirrhines, which include the lemurs, galagos, and lorisids, and the Haplorhini, haplorhines, which include the Tarsiiformes, tarsiers and ...

s, and is probably an

autapomorphic In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...

muscle unique to the human thumb (together with

flexor pollicis longus The flexor pollicis longus (; FPL, Latin ''flexor'', bender; ''pollicis'', of the thumb; ''longus'', long) is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. This muscle is uniq ...

) which probably evolved from the oblique portion of adductor pollicis. In

African apes Homininae (), also called "African hominids" or "African apes", is a subfamily of Hominidae. It includes two tribes, with their extant as well as extinct species: 1) the tribe Hominini (with the genus ''Homo'' including modern humans and numerou ...

, adductor pollicis is notably well-developed, with an origin on the carpus and its ligaments, and an insertion that has migrated distally, in some cases as far as the distal phalanx. The insertion of the PPIM into the extensor mechanism is likely to have evolved with tool usage in early hominids. As comparative anatomy studies of the human PPIM strongly suggest that the muscle is evolutionarily derived from the adductor pollicis, it has been proposed that PPIM should be designated by the name musculus adductor pollicis accessorius, which indicates that the muscle is most likely a de novo structure derived from the adductor pollicis.

Structure

Pollical palmar interosseous

Central palmar interossei

Innervation

Blood supply

Function

Other animals

Additional Images

See also

Notes

References