An anomalous muscle in the superficial region of the popliteal fossa, with special reference to its innervation and derivation.

An anomalous muscle was found in the superficial region of the right popliteal fossa in a 90-year-old Japanese female cadaver during dissection practice for medical students. The muscle ran transversely between the medial head of the gastrocnemius muscle and the tendon of the biceps femoris muscle, covering the nerves, vessels and muscle in the popliteal fossa. The muscle received its nerve supply from the common peroneal nerve. Based on the result of nerve fiber analysis, we speculated that the anomalous muscle might be close to the short head of the biceps femoris muscle in its derivation.