190 THE ARTICULATIONS OF THE LOWER LIMB. 



ridge of the fibula (fig. 142), and is composed for the most part of parallel fibres run- 

 ning outwards and downwards, only a few fibres crossing in a different direction. It 

 presents superiorly an elongated opening for the transmission of the anterior tibial 

 vessels, and inferiorly a small interval is left between it and the lower articulation 

 for the passage of the anterior peroneal vessels. 



Lower tibio-fibular articulation. The inferior extremities of the tibia and 

 fibula articulate by surfaces which for the most part are rough and bound together 

 by ligament, but at their lower part, for a distance of about a quarter of an inch, are 

 smooth and lined by synovial membrane. The tibial surface is concave, the fibular 

 is correspondingly convex. The strong short fibres which pass obliquely between 

 the opposed surfaces form the inferior inter osseous ligament (fig. 219, 4). The 

 anterior ligament (fig. 222, 2) is a flat band of fibres, extended obliquely over the 

 lower part of the bones, the direction of its fibres being downwards from the tibia to 

 the fibula. The posterior ligament is similarly disposed behind the articulation. 

 The transverse or inferior ligament is a short but thick band of yellowish fibres under 

 cover of the posterior ligament ; it runs horizontally from the hinder border of the 

 lower articular surface of the tibia to the contiguous part of the external malleolus, 

 and closes the angular interval between the bones. 



The synovial cavity of this articulation is an extension of that of the ankle-joint. 



THE ANKLE-JOINT. 



In this articulation, which is a hinge-joint, the inferior extremities of the tibia 

 and fibula are united so as to form a three-sided hollow, which embraces the astra- 

 galus : the socket is completed behind by the transverse ligament of the inferior 

 tibio-fibular articulation. The articular surface of the astragalus occupies the upper 



surface of the body, and is continued 

 downwards on each side of the bone 

 for the corresponding malleolus. The 

 inner margin of the superior surface 

 is nearly straight; the outer margin 

 is convex, and inclined inwards pos- 

 teriorly, thus making the surface 

 MALLEOLAR narrower behind than in front. Be- 



tween the upper and the external sur- 

 faces posteriorly is a narrow trian- 

 gular facet which plays against 

 the transverse tibio-fibular ligament. 

 The capsule of the articulation is 

 divided into the following 



INTERNAL 



ALLEOLAI 

 FACET 



T-,. 017 , The internal lateral or deltoid 



Fig. 217. THE ASTRAGALUS FROM ABOVE, SHOWING THE , 



ARTICULAR SURFACE AND THE ATTACHMENTS OP THE ligament (llg. 221, 1) IS a brOaO. 



LATERAL LIGAMENTS OF THE ANKLE-JOINT. (Drawn layer of fibres, which radiate from 



by T. W. P. Lawrence.) g the ^& malleolug to the fcargal 



bones. The hinder part is thick 



and short, and descends from the notch at the lower border of the malleolus to 

 the inner surface of the astragalus. The fore part, thinner and more expanded, 

 extends from the tip and anterior border of the malleolus to the sustentaculum 

 tali of the os calcis, the internal calcaneo-navicular ligament, and the dorsal surface 

 of the navicular bone. 



The external lateral ligament (fig. 222, 4, 5, 6) consists of three distinct 

 bands disposed in different directions. 1. The middle land descends from the 



