ANKLE JOINT 425 



foot at the ankle joint are the tibialis anterior, the extensor digitorum longus, 

 the extensor hallucis longus and the peronseus tertius ; those which 

 operate as plantar-flexors are the superficial muscles of the calf, the 

 tibialis posterior, the long flexors of the toes, and the peronseus longus 

 and brevis. 



TlBIO-FIBULAR JOINTS. 



The fibula articulates with the tibia by both its proximal 

 and its distal extremity. The proximal of the two joints, the 

 articulatio tibiofibularis, is a diarthrodial joint, possessing a 

 cavity and a capsule with accessory thickenings. The distal 

 joint is a syndesmosis, the syndesmosis tibiofibularis^ but in 

 some cases a prolongation of the cavity of the ankle joint 

 projects between the distal ends of the tibia and fibula 

 (Fig. 196). The interosseous membrane which occupies the 

 interval between the bodies of the bones may be regarded as 

 a ligament common to both joints. 



Dissection. Preparatory to the examination of the tibio- 

 fibular joints the foot must be removed by dividing the remains 

 of the ligaments on the medial and lateral aspects of the ankle 

 joint. The muscles also must be detached from both aspects 

 of the interosseous membrane and from the bones of the leg. 

 The ligaments may now be defined. 



Membrana Interossea Cmris. The interosseous mem- 

 brane is a strong membrane which stretches across the interval 

 between the two bones of the leg, and greatly extends the 

 surface for the origin of muscles. It is attached on the one 

 hand to the interosseous border of the tibia, and on the other 

 to the interosseous border of the fibula. It is composed of 

 strong oblique fibres, which take a direction distally and 

 laterally from the tibia to the fibula. In the proximal part 

 of the membrane, immediately distal to the lateral condyle 

 of the tibia, there is an oval opening for the passage of the 

 anterior tibial vessels, whilst a small aperture, a short distance 

 proximal to the ankle joint, marks the point where the 

 membrane is pierced by the perforating branch of the peroneal 

 artery. 



Articulatio Tibiofibularis (O.T. Superior Tibio-fibular Joint). 

 At the tibio-fibular joint the bones are held in apposition 

 by a capsule which is strengthened anteriorly and posteriorly. 

 The fibres of the strengthening bands pass, distally and 

 laterally, from the lateral condyle of the tibia to the head 



