|The mucous sheaths of the tendons around the ankle. Medial aspect. (Tendon of Plantaris labeled at bottom right.)|
|Gray's||subject #129 483|
|Origin||Lateral supracondylar ridge of femur above lateral head of gastrocnemius|
|Insertion||Tendo calcaneus (medial side, deep to gastrocnemius tendon)|
|Actions||Plantar flexes foot and flexes knee|
|Antagonist||Tibialis anterior muscle|
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 and mainly acts with gastrocnemius.
Origin and insertion 
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.
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 new medical students (and thus called the "freshman nerve"), the muscle was useful to other primates for grasping with their feet.
Additional information 
The plantaris is mainly used by surgeons for tendon grafts needed in other areas of the body. Although the plantaris does have little importance, there are injuries that can occur. It can be damaged in an Achilles tendon rupture. Tennis leg is a commonly known injury. It is a result of eccentric loading placed on the ankle while the knee is extended, and occurs while running or jumping. It may cause a direct trauma to the calf area. Pain and swelling are common in the injury. It is sometimes removed to treat its inflammation.
Additional images 
- DR. K. Musculoskeletal cases website: Plantaris tendon tear
- Moore, Keith L; & Dalley Arthur R (2008). Clinically Oriented Anatomy (6th ed.). Lippincott Williams and Wilkins. ISBN 978-1-60547-652-0
- LUC plnt
- SUNY Labs 15:st-0412
- -1274675120 at GPnotebook
- plantaris+%28muscle%29 at eMedicine Dictionary