264 THE ARTICULATIOXS 



superior aspect, where the l>order of the outer tuberosity of the tibia is bevelled 

 by the popliteus muscle, the joint is in the closest proximity to the bursa beneath 

 the tendon of that muscle, and is only separated from the knee-joint by a thin 

 septum of areolar tissue. There is often a communication between the synovial 

 cavities of the two joints. The ligaments uniting the bones are: — 



Capsular. Anterior tibio-fibular. 



Posterior tibio-fibular. 



The capsular ligament is a well-marked fibro-areolar structure; it is attached 

 close round the articular margins of the tibia and fibula. In front it is shut ofY 

 completely from the knee-joint by the capsule of the knee and the coronary liga- 

 ment; but liehind, it is often very thin, and may communicate with the bursa 

 under the popliteus tendon. 



The anterior tibio-fibular ligament (fig. 251) consists of a few fibres which 

 pass upwards and inwards from the fibula to the tibia. It lies beneath the anterior 

 portion of the tendon of the biceps. 



The posterior tibio-fibular ligament (fig. 245) consists of a few fibres w^hich 

 pass upwards and inwards between the adjacent bones, from the head of the fibula 

 to the outer tuberosity of the tibia. 



The superior interosseous ligament consists of a mass of dense yellow fibro- 

 areolar tissue, binding the opposed surfaces of the bones together for three-quarters 

 of an inch (2 cm. ) below the articular facets. It is continuous Avith the interosseous 

 membrane along the tibia. 



The biceps tendon is divided by the long external lateral ligament of the knee; 

 of the two divisions the anterior is by far the stronger, and is attached to the 

 external tuberosity of the tibia as well as to the front of the head of the fibula, and 

 thus the muscle, acting on both bones, tends to brace them more tightly together; 

 indeed, it holds the bones strongly together after all other connections have been 

 severed. 



The synovial membrane which lines the joint sometimes communicates with 

 the knee-joint through the bursa beneath the popliteus tendon. 



The arterial supply is from the inferior external articular and recurrent tibial 

 arteries. 



The nerve-supply is from the inferior external articular, and also from the 

 recurrent branch of the external popliteal. 



The movements are but slight, and consist merely of a gliding of the two 

 bones upon each other. The joint is so constructed that the fibula gives some 

 support to the tibia in transmitting 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 external 

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

 slightly upwards in flexion, and downwards in extension of the ankle. 



(/)) The Middle Tibio-fibular Union 



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

 and the interosseous border of the filnila. It is deficient above for about an inch 

 (2-5 cm.) 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 ai)oneurotic and translucent lamina, formed of oblicjue line fibres, 

 some of which run from the tibia to the lil)ula, and some from the fibula to the 

 tibia, but all are inclined downwards. They are best marked at their attachment 

 to the bones, and gradually groAv denser and thicker as they approach the inferior 

 interosseous ligament. The chief use of the membrane is to afford a surface for the 

 origin of muscles. It is continuous below with the inferior interosseous ligament. 



