THE TIBIOTARSAL ARTICULATION 345 



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. 



Synovial Membrane. The synovial membrane (Figr. 275) invests the inner surface of the 

 ligaments, and sends a duplicature upward between the lower extremities of the tibia and fibula 

 for a short distance. 



Relations. The tendons, vessels, and nerves in connection with the joint are, in front, from 

 within outward, the Tibialis anticus, Extensor proprius hallucis, anterior tibial vessels and 

 nerve, Extensor longus digitorum, and Peroneus tertius; behind, from within outward, the 

 Tibialis posticus, Flexor longus digitorum, posterior tibial vessels and nerve, Flexor longus 

 hallucis; and in the groove behind the external malleolus, the tendons of the Peroneus longus 

 and brevis. 



The arteries supplying the joint are derived from the malleolar branches of the anterior 

 tibial and the peroneal. 



The nerves are derived from the anterior and posterior tibial. 



Inferior tibiofibular articulation. 



Ankle-joint. 



Tarsal articulations. 



Tarsometatarsal 



articulations. 



FIG. 277. Ankle-joint: tarsal and tarsometatarsal articulations. External view. Right side. 



Movements. The movements of the joint are those of flexion and extension. Flexion con- 

 sists in the approximation of the dorsum of the foot to the front of the leg, while in extension 

 the heel is drawn up and the toes pointed downward. The malleoli tightly embrace the astragalus 

 in all positions of the joint, so that any slight degree of lateral movement which may exist is 

 simply due to stretching of the inferior tibiofibular ligaments and slight bending of the shaft of 

 the fibula. Of the ligaments, the internal is of very great strength so much so that it usually 

 resists a force which fractures the process of bone to which it is attached. Its middle portion, 

 together with the middle fasciculus of the external lateral ligament, binds the bones of the leg 

 firmly to the foot and resists displacement in every direction. Its anterior and posterior fibres 

 limit extension and flexion of the foot, respectively, and the anterior fibres also limit abduction. 

 The posterior portion of the external lateral ligament assists the middle portion in resisting the 

 displacement of the foot backward, and deepens the cavity for the reception of the astragalus. The 

 anterior fasciculus is a security against the displacement of the foot forward, and limits extension 

 of the joint. The movements of inversion and eversion of the foot, together with the minute 

 changes in form by which it is applied to the ground or takes hold of an object in climbing, etc., 

 are mainly effected in the tarsal joints, the one which enjoys the greatest amount of motion 

 being that between the astragalus and os calcis behind and the scaphoid and cuboid in front. 

 This is often called the transverse or mediotarsal joint, and it can, with the subordinate 

 joints of the tarsus, replace the ankle-joint in a great measure when the latter has become 

 ankylosed. 



