66 HANDBOOK OF ANATOMY 



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. 



The Ankle- Joint, between the upper, inner, and outer surfaces 

 of the astragalus and the lower ends of the tibia and fibula. 



It is a hinge joint, capable of movement round one axis only : 



Transverse flexion arid extension. 



Owing to the shape of the articular surface of the astragalus, 

 which is wider in front than behind, a slight side to side rocking 

 movement can be produced during extension, as in this position 

 the narrower portion of the astragalus is in the tibio-fibular 

 socket. During flexion the wider part of the astragalus is forced 

 into the socket, and the joint is, so to speak, " locked," and 

 inversion and eversion of the foot can only be performed by out- 

 side force. This movement takes place in the joint between the 

 cuboid and os calcis, and between the astragalus and scaphoid,, 

 not at all in the ankle-joint itself. 



A capsule completely surrounds the joint, and has various 

 strengthened parts. 



The Anterior ligament is a thin ligament attached above to the 

 anterior edge of the tibia, and below to the upper border of the* 

 head of the astragalus. A pad of fat fills the hollow between. 



