Transverse intermuscular septum

Overview
The deep transverse fascia of the leg (or transverse intermuscular septum) is a transversely placed, intermuscular septum, between the superficial and deep muscles of the back of the leg.

At the sides it is connected to the margins of the tibia and fibula.

Above, where it covers the Popliteus, it is thick and dense, and receives an expansion from the tendon of the Semimembranosus; it is thinner in the middle of the leg; but below, where it covers the tendons passing behind the malleoli, it is thickened and continuous with the laciniate ligament.