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) . It is composed of a thin muscle belly and a long thin tendon. It is approximately 2-4 inches long, and is absent in 7 - 10% of the human population. It is one of the plantar flexors in the superior compartment of the leg along with the gastrocnemius, and soleus. The plantaris is considered an unimportant muscle, it mainly acts with gastrocnemius[WP]. [ http://en.wikipedia.org/wiki/Plantaris_muscle ]