THE ANKLE-JOINT. 351 



This aperture (Fig. 317), which is about one inch long, adjoins the shaft of the 

 fibula at a point rather less than one inch distal to its head. Towards the distal 

 end of the leg the distance between the tibia and the fibula rapidly diminishes, and 

 consequently the width of the interosseous membrane is correspondingly reduced, 

 and it is tense throughout its entire length. In the distal part of the membrane 

 there is a small opening for the passage of the perforating peroneal vessels. There 

 is no sharply marked demarcation between the interosseous membrane and the 

 interosseous ligament which connects the distal ends of the tibia and fibula the 

 one, indeed, may be said to run into the other. 



Syndesmosis Tibiofibularis. The distal tibio-fibular joint is not on all occasions 

 provided with articular cartilage, so that it may either be a separate articulation, or 

 it may merely present a series of ligaments which are accessory to the (ankle-joint), 

 because it is clear that, under any circumstances, the object aimed at in this articu- 

 lation is to obtain additional security for the ankle-joint. The articular surface on 

 the tibia, when present, constitutes a narrow articular strip on the lateral side of 

 the distal end of the bone, and the joint-cavity is practically an upward extension 

 of the ankle-joint. The corresponding fibular facet is continuous with the ex- 

 tensive articular area, by means of which the fibula articulates with the talus. 

 By far the greater part of the opposing surfaces of tibia and fibula are, however, 

 non-articular and rough. 



The supporting ligaments are of great strength. 



Lig. Malleoli Lateralis Anterius. The anterior ligament of the lateral malleolus 

 (O.T. anterior inferior tibio-fibular ligament) (Fig. 322) consists of strong fibres which 

 pass obliquely distally and laterally from the front of the distal end of the tibia to 

 the front of the lateral malleolus. 



Lig. Malleoli Lateralis Postering. The posterior ligament of the lateral 

 malleolus (O.T. posterior inferior tibio-fibular ligament) (Figs. 321 and 322) is equally 

 strong, and passes in a similar direction between corresponding posterior surfaces. 



Lig. Malleoli Lateralis Distale. The distal ligament of the lateral malleolus 

 (O.T. transverse inferior tibio-fibular ligament) (Figs. 321 and 322) stretches between 

 the posterior border of the distal end of the tibia and the proximal end of the 

 pit on the medial and posterior aspect of the lateral malleolus. 



Ligamentum Interosseum. An interosseous ligament, powerful and some- 

 what extensive, connects the contiguous rough non -articular surfaces. Proximally, 

 as already mentioned, it is continuous with the interosseous membrane. Anteriorly 

 and posteriorly it comes into contact with the more superficial ligaments. Distally 

 it descends until it comes into intimate association with the articular cavity. 



A synovial stratum is found lining the small articular cavity, but it is always 

 a direct prolongation from that which lines the ankle-joint. 



AETICULATIONES PEDIS. 

 ARTICULATIO TALOCRURALIS. 



The ankle-joint is a ginglymus variety of a diarthrosis. The bones which enter 

 into its formation are the distal ends of the tibia and fibula, with the articular 

 areas on the superior, lateral, and medial surfaces of the talus. The tibia and 

 fibula, aided by the distal ligament of the lateral malleolus, form a three-sided socket 

 within which the talus is accommodated. The roof or most proximal part of the 

 socket, which is wider in front than behind, is formed, chiefly, by the quadri- 

 lateral articular surface on the distal end of the tibia, but towards its postero- 

 lateral margin the distal ligament of the lateral malleolus assists in its formation. 

 There also the tibial articular surface is continuous with the narrow articular 

 facet already described as forming part of the tibio-fibular syndesmosis. The 

 medial wall of the socket is formed by the articular facet on the lateral side of the 

 medial malleolus, and there is no interruption of the articular cartilage between 

 the roof and medial wall. The lateral wall of the socket is quite separate from 

 the foregoing parts, and consists of a large triangular facet upon the medial side 



