Put your arm on a flat surface, push your thumb against your pinky and tilt your hand slightly up. Do you see a raised band pop up in the middle of your wrist? If yes, you’ve got a vestigial muscle that connects to the palmaris longus, a muscle that is absent in about 10%-15% of the population. You might also have it on one arm but not the other.
Don’t worry if you are that 10%-15%; research has shown that the absence or presence of the muscle does not have any effect on grip strength. It is also a weak flexor and has no influence whatsoever over any wrist movements.
Studies have also shown that Asians (Chinese, Japanese, Indian, Turkish, Malaysian) are more likely to have an absence of the palmaris longus than the Caucasian populations (European and North American).
Hence, the palmaris longus is a ‘leftover’ muscle from our primate ancestors that serves no purpose in humans. In fact, it is one of the first tendon that surgeons will remove for grafting in cosmetic or reconstructive surgeries. The popularity of the tendon in grafting surgeries is due to the fact that there will be no physical deformities in the person after the operation. Using the patient’s own tendon is beneficial because it does not introduce any foreign objects into the body. If the palmaris longus is not present in an individual for harvesting, the plantaris muscle in the leg may be taken instead.
The palmaris longus can most commonly be found in mammals in varying lengths. It is especially developed in those that use their forelimbs to move around primarily. For the primates, this means that the palmaris longus is longer in lemurs and gibbons (since they do a lot of swinging around from tree to tree), while shorter in gorillas and chimpanzees (they don’t move around that much in treetops).
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