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 palmar or volar interossei (interossei volares in older literature) are four muscles, one on the thumb that is occasionally missing, and three small, unipennate, central muscles in the hand that lie between the

metacarpal bones In human anatomy, the metacarpal bones or metacarpus, also known as the "palm bones", are the appendicular bones that form the intermediate part of the hand between the phalanges (fingers) and the carpal bones ( wrist bones), which articulate ...

and are attached to the

index Index (: indexes or 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 the Halo Array in the ...

, ring, and little fingers. They are smaller than the

dorsal interossei of the hand In human anatomy, the dorsal interossei (DI) are four muscles in the back of the hand that act to abduct (spread) the index, middle, and ring fingers away from the hand's midline (ray of middle finger) and assist in flexion at the metacarpophal ...

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 The phalanges (: phalanx ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. Structu ...

and the extensor expansion 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 thumb ...

's medial side. Passing between the first dorsal interosseous and the oblique head of

adductor pollicis In human anatomy, the adductor pollicis muscle is a muscle in the hand that functions to Adduction, adduct the thumb. It has two heads: transverse and oblique. It is a fleshy, flat, triangular, and fan-shaped muscle deep in the Thenar eminence, ...

, it is inserted on the base of the thumb's proximal phalanx together with

. 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 Anatomy () is the branch of Morphology (biology), morphology concerned with the study of the internal structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things ...

since, but others have either failed to mention it or considered it part of either

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 ...

. 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 Greek word for 'sesame seed', indicating the small size of most sesamoids. Often, these bones form in response to strain, or can be presen ...

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 (carpus) that connects the hand to the forearm. The terms "carpus" and "carpal" are derived from the Latin wikt:carpus#Latin, carpus and the Greek language, Greek wikt:καρπός ...

, 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 (spelled fibre in British English; from ) 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 inco ...

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 band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

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 terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, Limb (anatomy), limbs, and specific sections of the body. The terminology used de ...

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 is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...

s, and is probably an autapomorphic muscle unique to the human thumb (together with flexor pollicis longus) which probably evolved from the oblique portion of adductor pollicis. In

African apes Homininae (the hominines) is a subfamily of the family Hominidae (hominids). (The Homininae——encompass humans, and are also called "African hominids" or "African apes".) This subfamily includes two tribes, Hominini and Gorillini, both havin ...

, 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