378 



THE ARTICULATIONS. 



anticus and Peroneus tertius, and the anterior tibial vessels and nerve ; behind, it 

 lies in contact with the synovial membrane. 



The Posterior Tibio-tarsal Ligament is very thin, and consists principally of 

 transverse fibres. It is attached, above, to the margin of the articular surface of the 

 tibia, blending with the transverse tibio-fibular ligament ; below, to the astragalus, 

 behind its superior articular facet. Externally it is thicker than internally, where 

 a somewhat thickened band of transverse fibres is attached to the hollow on the 

 inner surface of the external malleolus. 



The Internal Lateral or Deltoid Ligament is a strong, flat, triangular band, 

 attached, above, to the apex and anterior and posterior borders of the inner mal- 

 leolus. The most anterior fibres pa.ss forward to be inserted into the navicular 

 bone and the inferior calcaneo-navicular ligament ; the middle descend almost 

 perpendicularly to be inserted into the sustentaculum tali of the os calcis ; and the 

 posterior fibres pass backward and outward to be attached to the inner side of the 

 astragalus. This ligament is covered by the tendons of the Tibialis posticus and 

 Flexor longus digitorum muscles. 



Inferior tibio-fibular articulation. 



Ankle-joint. 



Tarsal articulations. 



Tarso-metatarsal 



articulations. 



FIG. 264. Ankle-joint : tarsal and tarso-metatarsal articulations. External view. Right side. 



The External Lateral Ligament (Fig. 264) consists of three distinctly special- 

 ized fasciculi of the capsule, taking different directions and separated by distinct 

 intervals ; for which reason it is described by some anatomists as three distinct 

 ligaments. 1 



The anterior fasciculus (anterior astragalo-fibular), the shortest of the three, 

 passes from the anterior margin of the summit of the external malleolus, downward 

 and forward, to the astragalus, in front of its external articular facet. 



The posterior fasciculus (posterior astragalo-fibular), the most deeply seated, 

 passes from the depression at the inner and back part of the external malleolus 

 to a prominent tubercle on the posterior surface of the astragalus. Its fibres are 

 almost horizontal in direction. 



The middle fasciculus (calcaneo-fibular), the longest of the three, is a narrow, 

 rounded cord passing from the apex of the external malleolus downward and 

 slightly backward to a tubercle on the outer surface of the os calcis. It is covered 

 by the tendons of the Peroneus longus and brevis. 



1 Humphry, On the Skeleton, p. 559. 



