The contrahentes (singular contrahens) are

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

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

distal 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. Structur ...

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 ...

big toe Toes are the Digit (anatomy), digits of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being ''digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being ' ...

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

, which suggests that the

palmar interossei muscles In human anatomy, 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 Metacarpus, me ...

also contain elements of the contrahentes. They appear in the human fetus as a layer of flesh that 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 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. Struct ...

they facilitate convergence of the digits. In

tarsier Tarsiers ( ) are haplorhine primates of the family Tarsiidae, which is the lone extant family within the infraorder Tarsiiformes. Although the group was prehistorically more globally widespread, all of the existing species are restricted to M ...

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 ...

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