296 THE ARTICULATIONS 



the weight to the foot. The articular facet of the tibia overhangs, and is received upon the 

 articular facet of the head of the fibula in an oblique plane. This joint allows of slight yielding 

 of the lateral malleolus during flexion and extension of the ankle-joint, the whole fibula gliding 

 slightly upward in flexion, and downward in extension, of the ankle. 



(6) The Middle Tibio-fibular Union 

 Class. — Synarthrosis. Subdivision. — Syndesmosis. 



The interosseous membrane is attached along the lateral border of the tibia 

 and the interosseous border of the fibula. It is deficient above for about 2.5 cm. 

 (1 in.) or more, measured from the under aspect of the superior joint. Its upper 

 border is concave, and over it pass the anterior tibial vessels. 



The membrane consists of a thin aponeurotic and translucent lamina, formed of oblique 

 fine fibres, some of which run from the tibia to the fibula, and some from the fibula to the tibia, 

 but all are inclined downward. They are best marked at their attachment to the bones, and 

 gradually grow denser and thicker as they approach the inferior interosseous ligament. The 



Fig. 328. — Lower Ends of Left Tibia and Fibula, showing the Ligaments. The synovial 

 fold between these bones has been removed to show the transverse Ugament forming part 

 of the capsule of the joint, and the deeper fibres of the anterior lateral malleolar Hgament 

 which come into contact with the talus. 

 (From a dissection by Mr. W. Pearson, of the Royal College of Surgeons' Museum.) 



1 Anterior lateral malle- 

 _ / olar ligament 



' Lateral ligament 



^ - Transverse ligament 



Deltoid ligament Yv^^i^§W--^ -/ ^ y^ '"" ^^^^'^'^ Posterior lateral malle- 



^ olar ligament 



chief use of the membrane is to afford a surface for the origin of muscles. It is continuous below 

 with the inferior interosseous ligament. 



In front of the interosseous membrane lie the tibialis anterior, the extensor digitorum longus, 

 the extensor hallucis longus, and the anterior tibial vessels and nerves. Behind it is in relation 

 with the tibialis posterior, the flexor hallucis longus, and the peroneal artery. 



(c) The Inferior Tibio-fibular Articulation 

 Class.- — Diarthrosis. Subdivision. — Arthrodia. 



This junction is formed by the lower ends of the tibia and fibula. The rough 

 triangular surface on each of these bones formed by the bifurcation of their 

 interosseous lines is closely and firmly united by the inferior interosseous liga- 

 ment. The fibula is in actual contact with the tibia by an articular facet, which 

 is small in size, crescentic in shape, and continuous with the articular facet of 

 the malleolus. 



The ligaments which unite the bones are: — 



1. Anterior lateral malleolar ligament. 



2. Posterior lateral malleolar ligament. 



3. Transverse ligament. 



4. Inferior interosseous ligament. 



The anterior lateral malleolar ligament (anterior inferior tibio-fibular liga- 

 ment) (figs. 328 and 334) is a .strong triangular band about 2 cm. (f in.) wide, 

 and is attached to the lower extremity of the tiljia at its anterior and lateral 

 angle, close to the margin of the facet for the talus and passes downward and 



