The tendon that is commonly missing in the hand is called the palmaris longus. The palmaris longus is a small tendon that is located between the flexor carpi radialis and the flexor carpi ulnaris muscles in the forearm. It is often referred to as a vestigial muscle, meaning that it no longer serves a significant function in human anatomy.
Interestingly, the presence or absence of the palmaris longus tendon varies among individuals. Studies have shown that approximately 14 percent of the population lack this tendon in one or both hands. However, it is important to note that the absence of the palmaris longus tendon can vary among different populations. For instance, some research suggests that the prevalence of its absence may be higher in African, Asian, and Native American populations compared to other ethnic groups.
The variation in the presence of the palmaris longus tendon can be attributed to genetic factors. It is believed that the absence of this tendon is an evolutionary adaptation that has occurred over time. In our ancestors, the palmaris longus muscle may have played a role in strengthening grip and aiding in activities such as climbing or swinging from trees. However, as humans have evolved and our lifestyles have changed, the need for this muscle has diminished, leading to its gradual disappearance in some individuals.
In terms of functionality, the absence of the palmaris longus tendon does not usually cause any significant issues or impair hand function. Most individuals who lack this tendon are completely unaware of its absence and lead normal lives without any limitations. Other muscles and tendons in the hand are able to compensate for the absence of the palmaris longus, ensuring that hand movements and grip strength are not compromised.
To determine the presence or absence of the palmaris longus tendon, a simple clinical test called the “palmaris longus test” can be performed. This test involves flexing the wrist and touching the thumb to the little finger while keeping the other fingers extended. If the tendon is present, a small prominence or bulge can be seen and felt in the wrist area. However, if the tendon is absent, there will be no visible or palpable bulge.
The palmaris longus tendon is commonly missing in the hand, with approximately 14 percent of the population lacking it. Its absence is believed to be an evolutionary adaptation and does not usually cause any functional limitations. The variation in the presence of this tendon among different populations adds an interesting aspect to the study of human anatomy and genetics.