The contrahentes (singular contrahens) are

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

s widely present in the hands of mammals, including monkeys. They are on the palmar/plantar side. There is one each for digits I, II, IV and V, but not III. They pull the fingers/toes down and together.

Human anatomy

In humans, the

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

in the hand and the

adductor hallucis The Adductor hallucis (Adductor obliquus hallucis) arises by two heads—oblique and transverse and is responsible for adducting the big toe. It has two heads, both are innervated by the lateral plantar nerve. Structure Oblique head The ''oblique ...

in the foot are well-developed remnants of the first contrahens, though they have lost the insertion on the distal phalanx of 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 ...

or big toe. The other contrahentes only appear as rare

atavistic In biology, an atavism is a modification of a biological structure whereby an ancestral genetic trait reappears after having been lost through evolutionary change in previous generations. Atavisms can occur in several ways; one of which is when ...

abnormalities. In other mammals, the contrahentes may have their origin either on the carpus or the metacarpus, which suggests that the

palmar interossei muscles In human anatomy, the palmar or volar interossei (interossei volares in older literature) are three small, unipennate muscles in the hand that lie between the metacarpal bones and are attached to the index, ring, and little fingers. They are small ...

also contain elements of the contrahentes. They appear in the human fetus as a layer of flesh which mostly disappears.

In other animals

The contrahens of the fourth digit is absent in dogs but present in cats and rabbits. In primates, the contrahentes vary in number between zero and four. By their insertion onto the proximal phalanges they facilitate convergence of the digits. In

tarsier Tarsiers ( ) are haplorhine primates of the family Tarsiidae, which is itself the lone extant family within the infraorder Tarsiiformes. Although the group was once more widespread, all of its species living today are found in Maritime Southeast ...

s, they facilitate the grip by increasing the pressure between the large distal pads and the gripped surface by simultaneously flexing 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 cav ...

s and the proximal

interphalangeal joints Interphalangeal joint may refer to: *Interphalangeal articulations of hand The interphalangeal joints of the hand are the hinge joints between the phalanges of the fingers that provide flexion towards the palm of the hand. There are two sets in ...

and extending the distal interphalangeal joints.

Notes

References

* * * * {{Muscles of lower limb Muscles of the upper limb Hand Muscles of the lower limb Foot