contrahentes
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The contrahentes (singular contrahens) are muscles 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 beneath ...
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 or big toe. The other contrahentes only appear as rare atavistic 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 sm ...
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 tarsiers, 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 ca ...
s and the proximal interphalangeal joints and extending the distal interphalangeal joints.


Notes


References

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