THE BONES OF THE LEG AS ONE APPARATUS. 



397 



tially ligamentous, though the articular cartilage of the ankle-joint extends for a few 

 millimetres onto the opposed sides of each bone. 



The inferior ligaments are the interosseous, the anterior ^n6. posterior, and the 

 tratisverse. The interosseous ligament is a thickened continuation of the mem- 

 brane, consisting of short fibres connecting the rough surfaces bounded by the split- 

 ting of the interosseous ridges. 



The anterior and posterior liga77ients^ (Fig. 411, 412) are strong bands situ- 

 ated respectively on the front and the back of the tibia and running downward and 

 outward to the fibula. The anterior deepens the socket but slighdy, while the 

 posterior, reaching nearly half-way down to the malleolus, makes a considerable 

 addition to the back of the joint. The transverse ligament (Fig. 412) containing 



Fig. 412. 



Ant. tibio-fibular ligament 



Capsule reflected 



Ant. lateral ligament 



Middle lateral ligament 



Outer malleolus 



Deltoid ligament 



Transverse ligament 



Pad of fat 

 Post, external lateral ligament 



Capsule 

 Post, tibio-fibular ligament 



Socket of right ankle-joint from below. 



probably elastic fibres, runs obliquely from the back or the lower border of the 

 tibia to the tip of the outer malleolus. It projects into the joint, the capsule form- 

 ing a pouch between it and the posterior tibio-fibular ligament. It is closely con- 

 nected at the fibula with the posterior fibulo-astragaloid ligament. The two have 

 the appearance of diverging bundles of the same structure. The synovial cavity is 

 prolonged some three millimetres upward between the bones. The back part of the 

 crack between the bones is concealed by a pad of fat (Fig. 412) covered by 

 synovial membrane projecting into the joint. It advances or recedes between the 

 bones according to changes of position. 



Movements. — The motions between the tibia and the fibula are slight and 

 not very definite. The head of the fibula may play a little forward and backward, 

 and the bone may rotate on its long axis. These motions are resisted alternately 

 by the anterior and posterior ligaments at both ends. 



THE BONES OF THE LEG AS ONE APPARATUS. 

 Surface Anatomy. — The upper part of this support consists of the head of 

 the tibia with that of the fibula well back on the outer side. The framework nar- 

 rows to the junction of the middle and lower thirds, where the tibia is nearly at its 

 smallest and seems to bend towards the fibula. Below this it broadens for the 

 socket of the ankle. The fibula in the lower third is close to the tibia and no longer 

 so much behind it, which is due in part to the subsidence of the crest of the tibia. 

 The difference of relations is shown by sections at three levels (Fig. 413). The 

 whole apparatus is described as having three borders and three surfaces. As the 

 details have been given with the bones, the chief features only are here enumerated. 

 The anterior border is the crest of the tibia ; the posterior and internal border is the 

 posterior border of the same bone; between them is the subcutaneous internal surface. 

 The posterior and external border is the postero-external border of the fibula. Thus 

 there remain an antero-external and a posterior surface each of which is formed in 



' Ligg. malleoli lateralis anterius at posterius. 



