The Gastrocnemius muscle is a fusiform, two headed, two joint muscle. The two heads of origin are lateral and medial head taking origin from medial and lateral condyles of femur respectively. In between the two heads tibial nerve passes. Inferiorly it forms a common tendon with the Soleus and Plataris muscles; this tendon is known as the Tendocalcaneus or Achilles tendon which get inserted to posterior surface of Calcaneum. The case was reported during routine dissection for undergraduate B.A.M.S. students at National Institute of Ayurveda Deemed University, Jaipur. The subject was 36-year-old male cadaver of North Indian origin. The accessory head was observed during the cadaveric dissection of the popliteal fossa.

The Gastrocnemius muscle was bulky. The inferolateral and inferomedial boundary of the Popliteal fossa were made by medial and lateral head of Gastrocnemius. In addition to the normal medial and lateral head an accessory head of Gastrocnemius was seen bilaterally. The accessory head (Gastrocnemius tertius ) having two bellies, superficial and deep were observed in the both lower extremity. The superficial belly of the Gastrocnemius tertius muscle had its origin from an area just above the tendon of the plantaris muscle, the deep belly from the tendon of the plantaris muscle and inserted to the lateral head of the Gastrocnemius muscle. All the heads were innervated by branches from tibial nerve. It is possible that this variant muscle could have a compressive effect on the tibial nerve and popliteal vessels, and the awareness of this may prevent its misinterpretation as a pathological structure by radiologists and surgeons.