Soleus & Plantaris Muscle

Illustration from 'Surgical Anatomy: The Treatise of the Human Anatomy and Its Applications to the Practice of Medicine and Surgery, volume III' (by Dr. John Blair Deaver) shows the plantaris, a very small muscle which has the longest tendon of any muscle in the body, and is representative of the palmaris longus of the forearm, 1903. It assists the gastrocnemius, being an extensor of the ankle if the foot be not fixed, and a flexor of the knee when acting from its point of insertion. The soleus is a large flat muscle arising by two heads. The outer head arises from the posterior surface of the head of the fibula and from the upper part of the posterior and internal surface of the shaft of the same bone. The inner head arises from the oblique line of the tibia, from the middle third of the inner border of the tibia, and from a tendinous arch between the tibia and fibula. It is an extensor of the ankle. . (Photo by VintageMedStock/Getty Images)