The |plantaris| is a very small muscle that lies between the |gastrocnemius| and |soleus| muscles. It runs from the lower end of the |femur| (upper leg bone) to a small area on the bottom of the calcaneum (heel bone). The belly of the muscle is about three or four inches in length and tapers into a long, slender ~tendon~ that crosses between the two muscles of the calf and continues to the |calcaneus|. This muscle works with the |gastrocnemius| to extend the ankle if the foot is free and bend the knee if the foot is fixed, as when walking.