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Crus (leg) posterior compartment muscles
The large posterior compartment of the leg, often called the calf, is approximately four to five times more massive then the combined anterior and lateral compartments. Like the posterior thigh, this musculature arises from the embryonic anterior, or flexor, muscle of the embryo. All the muscles receive their nerve supply from the tibial nerve via the anterior divisions of the sacral plexus. The compartment has a large superficial group of muscles that share a common attachment on the calcaneus via the large calcaneal (Achilles) tendon. This tendon is the largest and strongest tendon in the body and can be easily palpated as the large cable-like structure at the back of the ankle. Beneath the superficial muscles lies a deeper group of muscles that are the antagonistic flexor counterparts to the muscles of the anterior leg compartment. These deep muscles pass behind the medial malleolus, under the cover of a retinaculum, to the plantar surface of the foot. The common action shared by the superficial and deep muscles is plantar flexion of the ankle joint.