Bodily Oddities

Plantaris muscle

Also called: Freshman's nerve

A small calf muscle with a very long, thin tendon that medical students mistake for a nerve. Between 7% and 20% of people do not have it.

Muscle Variation Structural
Vestigial

How common

Missing in 7–20% of people Common · 10–50%

Do you have this?

These are answers from visitors, not a study.

How it works

The plantaris is a small muscle at the back of the knee. Its belly is only 7 to 10 centimetres long1. Its tendon is another matter. It runs down the whole calf between the two large calf muscles and joins the Achilles tendon near the heel1. It is one of the longest tendons in the body.

In animals that grip with their feet, the plantaris helps to flex the toes. In humans the tendon no longer reaches the toes, and the muscle adds very little to pushing off the ground1. It is listed as vestigial for that reason2. It may still have a role as a sensor. The muscle is rich in stretch receptors, so it may report the position of the ankle to the brain1.

Between 7% and 20% of people do not have it on one or both legs1. Missing it has no known effect on walking, running, or jumping. Surgeons use the tendon as spare material for repairing tendons in the hand and foot1.

The muscle can tear during a sudden push-off in sport. This is sometimes called tennis leg. It hurts, but it heals without surgery1.

History and culture

The tendon is thin, pale, and cord-like. First-year medical students often mistake it for a nerve in dissection classes, which is why it is nicknamed the freshman’s nerve1.

Sources and further material

  1. Encyclopedia Plantaris muscle
  2. Encyclopedia Vestigiality
  3. Video Plantaris muscle anatomy YouTube search.
Muscle Variation

Palmaris longus

A thin tendon that stands out in the wrist when you press your thumb and little finger together. About 1 in 7 people do not have it at all, and they lose nothing.

Missing in about 15% of people
Ears Variation

Darwin's tubercle

A small bump on the folded rim of the ear, which Darwin thought was the leftover tip of a pointed ancestral ear. Between 10% and 58% of people have one, depending on the population.

10–58% of people
Bones Variation

Accessory ossicles

Small extra bones, most often in the foot, that form when a growth centre never fuses with its main bone. They are harmless but can be mistaken for fractures on an X-ray.

Up to 1 in 5 feet