Palmaris Longus

The palmaris longus is seen as a small tendon between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present.

It is a slender, fusiform muscle, lying on the medial side of the flexor carpi radialis.

Anatomy of the Palmaris Longus

The palmaris longus muscle is antagonist to the Extensor carpi radialis brevis, Extensor carpi radialis longus and the Extensor carpi ulnaris.

It is innervated by the median nerve and supplied by the ulnar artery.

The palmaris longus arises from the medial epicondyle of the humerus by the common flexor tendon, from the intermuscular septa between it and the adjacent muscles, and from the antibrachial fascia.

It ends in a slender, flattened tendon, which passes over the upper part of the flexor retinaculum, and is inserted into the central part of the flexor retinaculum and lower part of the palmar aponeurosis, frequently sending a tendinous slip to the short muscles of the thumb.

The palmaris longus is a variable muscle, absent in about 16 percent of Caucasians, and less frequently absent in other populations.

It may be tendinous above and muscular below; or it may be muscular in the center with a tendon above and below; or it may present two muscular bundles with a central tendon; or finally it may consist solely of a tendinous band. The muscle may also be double.

Functions of the Palmaris Longus

The palmaris longus tendon is responsible for exposing the claws in lower vertebrates. In humans, it acts as a wrist flexor.

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