The Tibio-Fibular Joints are two in number, between the opposing surfaces of the extremities of the tibia and fibula. The fibula forms a lateral support for the ankle-joint, and is not required to have any independent movement, so these joints simply provide a certain amount of elasticity, and are slightly gliding.

The Superior Tibio-Fibular Joint is formed between the small oval facet on the inner surface on the head of the fibula, and the facet on the posterior part of the external tuberosity of the tibia. It is surrounded by a capsule and several strengthening ligaments, more or less defined.

The synovial membrane is sometimes continuous with that of the knee-joint.

The Inferior Tibio-Fibular Joint is formed between the opposing surfaces of the lower ends of the tibia and fibula; this is not always a separate joint, but may be only a series of ligaments accessory to the ankle-joint. The ligaments are particu-larlv strong.

The Anterior Inferior Tibio-Fibular ligament is a strong band of fibres attached to the front of the lower end of the tibia and the outer malleolus.

The Posterior Inferior Tibio-Fibular ligament is also a strong band of fibres attached similarly on the posterior aspect of the bones.

The Transverse Inferior Tibio-Fibular ligament is attached to the posterior inferior border of the tibia, and the pit or fossa on the posterior part of the inner surface of the external malleolus.

The Interosseous ligament connects the opposing surfaces; it is continuous above with the interosseous membrane, and attached in front and behind to the ligaments.

The synovial membrane lining the joint cavity is continuous with that of the ankle-joint.

The Interosseous membrane attached to the interosseous borders may be considered an accessory ligament to these joints. It joins the inferior tibio-fibular joint below and may join the superior tibio-fibular joint above, but there is always an opening in its upper part for the anterior tibial vessels. Its fibres are mainly directed downwards and outwards.