Muscles of the posterior surface of knee joint and calf
These specimens show the superficial and deep muscles of the back of the leg.
Superficial muscles in the back of the leg are the gastrocnemius (medial and lateral heads), the soleus and the plantaris. The deep muscles in the back of the leg are the popliteus, the flexor digitorum longus, the flexor hallucis longus and the tibialis posterior. The thickest tendon of the body, that is, the tendocalcaneus can be identified.
The gastrocnemius has two heads, namely, the medial and the lateral heads. Both heads are supplied by the tibial nerve. Both heads take origin from the lower end of femur. The gastrocnemius along with the soleus, is known as the triceps surae. The triceps surae form the tendocalcaneus and insert into the calcaneum. It is the chief plantar flexor of the foot at the ankle joint.
The soleus is a sole-shaped muscle, located deep to the gastrocnemius. Its origin lies at the upper part of posterior aspect of shaft of tibia and fibula. The soleus, along with the gastrocnemius is known as the triceps surae. The triceps surae form the tendocalcaneus and insert into the calcaneum. It is the chief plantar flexor of the foot at the ankle joint. The soleus is regarded as the peripheral heart because the venous sinuses in it communicates with the superficial and the deep veins. Therefore, contraction of the soleus directs the blood from the superficial to the deep veins, thus facilitating the venous return.
The tendocalcaneus (Achilles tendon), is the thickest and the strongest tendon of the body. It is almost fifteen centimeters long. It is a conjoint tendon formed by the two heads of gastrocnemius and soleus muscles. It inserts into the dorsal surface of the middle one third of the calcaneum. It facilitates the plantar flexion of the foot at the ankle joint.
The plantaris is a unique muscle. It has a small muscle belly and a very long, slender tendon. The muscle belly originates from the lower end of the lateral supracondylar line of the femur (along with the lateral head of gastrocnemius) and the long slender tendon inserts into the calcaneum along with the tendocalcaneus. It is supplied by the tibial nerve. The tendon is generally used as a tendon graft for the repair of worn out/ damaged tendons. Thus muscle would be absent in about 5%-10% of people.