Abstract
The frequencies of the gastrocnemius tertius muscle existence differ from race to race (2.9% in the white, 3.4% in the black and 4.6% in Japanese). From phylogenical point of view, gastrocnemius tertius muscle is a very interesting muscle and has the comparatively low frequencies. Authors recognized this variational muscle in three cases (5.0±2.8%) out of thirty cadavers (Male : 16 cadavers, Female : 14 cadavers) with sixty side cases of Japanese adults as follows ; Case 1 : Female, 38 yr., Left. The origin of this muscle is the popliteal surface of femur which is located in the slightly inside of the origin of gastrocnemius's medial head. It becomes a narrow insertal tendon and reaches to the inside edge of lateral head. The innervation is the same one as lateral head's. Case 2 : Male, 45 yr., Right. The origin of this muscle is the inside of medial head. The insertion is the inner edge of medial head and the innervation is the same one as medial head's. Case 3 : Male, 68 yr., Left. The origin of this muscle is one third from the outside of popliteal surface of femur. Most of insertal tendon stops at the inner edge of lateral head and a part of it reaches to the inner edge of medial head. The innervation is the same one as medial head's. Regarding to the innervation, all cases coinside with SATO's hypothesis (1984) as gastrocnemius tertius nerve branches out from the nerve of gastrocnemius's head which comes out from the side of proximal and superficial layer of tibial nerve. Besides, suppliting arteries of each case come out either from the independent branch or the artery of gastrocnemius's head which is at the same side of the independent branch and both are from popliteal artery.
