Plantaris muscle

Plantaris is a vestigial structure and one of the superficial muscles of the posterior crural compartment of the leg.

It is innervated by the tibial nerve (S1, S2).

Origin and insertion
It arises from the inferior part of the lateral supracondylar line of the femur at a position slightly superior to the origin of the lateral head of gastrocnemius.

Also, it may arise from the oblique popliteal ligament.

Passing inferomedially posterior to the knee joint, it becomes tendinous while passing distally to insert into the tendo calcaneus, or occasionally separately inserting into the medial side of the calcaneus.

Functions
Plantaris acts to weakly:


 * plantarflex the ankle joint
 * flex the knee joint

Plantaris may also provide proprioceptive feedback information to the central nervous system regarding the position of the foot. The unusually high density of proprioceptive receptor end organs supports this notion.

Its motor function is so minimal that its long tendon can readily be harvested for reconstruction elsewhere with little functional deficit. "Often mistaken for a nerve by freshman medical students, the muscle was useful to other primates for grasping with their feet. It has disappeared altogether in 9 percent of the population."