The posterior compartment of the leg muscles consists of superficial and deep muscles. The superficial layer of the posterior compartment of the leg includes the following muscles:

Triceps surae muscle, consisting of:
- Gastrocnemius muscle
- Soleus muscle
Plantaris muscle (visualization shown in the next slide)

Triceps surae

The triceps surae muscle forms the main mass of the calf and consists of two superficial muscles: gastrocnemius muscle and soleus muscle. The gastrocnemius consists of two heads, and the soleus lies under the gastrocnemius.

Each muscle of the triceps surae has a different site of origin, but insertion tendons of both muscles join in the midline of the leg forming one tendon, which inserts into the calcaneal tuberosity. The common tendon of the triceps surae is called the Achilles tendon (or calcaneal tendon).

The triceps surae provides flexion, supination and adduction of the foot, while the gastrocnemius also provides flexion at the knee joint, as well as internal and external rotation of the knee.

Gastrocnemius

The gastrocnemius muscle is a superficial muscle situated in the posterior aspect of the lower leg. It originates with two heads - medial and lateral.

Origin: medial head - medial condyle of the femur, lateral head - lateral condyle of the femur.

Insertion: both of its heads join in the midline of the lower leg in a tendon (Achilles tendon), which inserts into the posterior surface of the calcaneus.

Action: flexion of the leg, plantar flexion of the foot.

Innervation: tibial nerve (S1 - S2).

Blood supply: sural arteries.

Soleus

The soleus muscle is a powerful muscle belonging to the posterior group of the lower leg muscles.

Origin: head of the fibula, upper third of the posterior border of the fibula, and soleal line of the tibia, middle third of the medial tibial border, tendinous arch between the fibula and tibia.

Insertion: the soleus muscle joins with the tendons of the gastrocnemius muscle, forming the calcaneal tendon or Achilles tendon that inserts into the posterior surface of the calcaneus.

Action: plantar flexion of the foot; this muscle also plays an important role in maintaining the standing pose.

Innervation: tibial nerve (S1 - S2).

Blood supply: sural arteries and peroneal (fibular) artery, branches of the posterior tibial artery.

Plantaris

The plantaris muscle is a superficial muscle of the posterior group of the lower leg muscles. The plantaris has a belly and a long thin tendon. (see the visualization in the next slide)

Origin: lateral supracondylar line of the femur, oblique popliteal ligament of the knee joint.

Insertion: the muscle passes inferomedially and inserts into the Achilles tendon (which inserts into the posterior surface of the calcaneus) or the muscle independently inserts into posterior calcaneus.

Action: the plantaris plays a role in flexion of the knee, and plantarflexion of the foot.

Innervation: tibial nerve (S1 - S2).

Blood supply: branches of the popliteal artery and posterior tibial artery.

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Superficial posterior compartment of leg muscles