Gastrocnemius muscle

The gastrocnemius muscle is a muscle of the pelvic limb located caudally to the tibia and the stifle joint. It is composed of two almost symmetrical heads. It forms the triceps surae muscle with the soleus muscle.

Conformation: The two heads are thick, fleshy bodies flattened on both sides. They are broad in the middle and narrow distally and proximally. The medial one is usually larger. They are broad in the middle section, narrowing distally and proximally. Particularly distally, where their strong common tendon starts and joins the common calcaneal tendon. Their proximal end narrows less but becomes almost entirely fibrous near its origin on the femur.

Origin: The lateral head arises by a large tendon on the lateral supracondylar tuberosity of the femur and the medial head arises on the medial supracondylar tuberosity.

Insertion: Via the common calcaneal tendon to the calcaneal tuberosity.

Relations: The fleshy bodies are covered by the deep crural fascia and hidden by the caudal femoral muscles. Both heads cover the flexor digitorum superficialis muscle, which adheres to the lateral head. They also cover the popliteal muscle, the popliteal vessels, the deep flexor muscles of the digits and, in some species, part of the soleus muscle. The tibial nerve passes between the two heads. The common fibular nerve runs along the lateral side of the lateral head. Before joining the common calcaneal tendon, its tendon is bypassed by the tendon of the flexor digitorum superficialis muscle and enveloped by extensions of the crural fascia.

Action: Primarily extends the tarsal joint; slight flexion of the stifle joint.

Vascularization: Subdivisions of the popliteal artery and caudal femoral arteries

Nerve: Tibial nerve

Description: The gastrocnemius muscle is located in the caudal part of the crus. Formed by two large flat fleshy bodies that meet distally in a thick tendon that joins the common calcaneal tendon. Its contraction causes the tarsal joint to extend and a slight flexion of the stifle joint due to its insertion on the calcaneal tuberosity. Each of these heads originates from the supracondylar tuberosities of the femur through a particularly fibrous zone that may present a nucleus of ossification in some species. In carnivores and rabbits, this nucleus creates a sesamoid bone articulated to the femoral condyle. The two heads cover the flexor digitorum superficialis muscle, whose tendon bypasses the tendon of the gastrocnemius muscle before joining the common calcaneal tendon. The popliteus muscle, the deep flexor muscles of the digits, and sometimes part of the soleus muscle are also covered by this large muscle. This muscle is itself covered by the caudal femoral muscles. Blood supply is provided by vessels from the popliteal and caudal femoral arteries. The tibial nerve passes between its two heads and innervates this muscle via minor branches.

Variations:

• In equines, this muscle is less voluminous in proportion compared to other species. The flexor digitorum superficialis muscle lies between the two heads of the gastrocnemius muscle. The origins of the two fleshy bodies are higher on the femur than in other species, and the supracondylar tuberositys are particularly pronounced.