OSTEOLOGY AND SYNDESMOLOGY. 43 



each are fibrous, and fixed to the head of the tibia by insertions known as 

 the oblique ligaments. They serve to deepen the articular surfaces of the 

 tibia, and thus to retain the condyles of the femur. They also lessen the 

 effect of concussion in the joint and in the limb generally. 



4. Superior Tibio-fibular Articulation. But little motion exists 

 between the tibia and fibula at their superior extremities : the joint is, how- 

 ever, secured by a distinct synovial membrane, sometimes communicating 

 with that of the knee joint ; there is also a distinct anterior and posterior 

 ligament, the former of which is the stronger. 



5. Inferior Tibio-fibular Articulation. Here the inferior extremity 

 of the fibula is convex, and received into a depression on the tibia : both 

 surfaces are rough superiorly, and covered by cartilage inferiorly : they 

 are connected with each other b}' a strong anterior and posterior ligament. 

 The synovial membrane is only a small cul de sac continued from that of the 

 ankle joint. Above this is the interosseous ligament, which fastens the 

 bones very closely and firmly together. Very little motion occurs in this 

 joint beyond a slight yielding of one surface against the other. 



6. Articulation of the Ankle {pi. 126, figs. 13, 14). This is the 

 most perfect ginglymoid or hinge joint in the body, excepting that between 

 the ulna and humerus. A deep mortice-like cavit}^, with an antero-poste- 

 rior edge, is formed by the lower surface of the tibia, and by the two 

 malleoli. The fibula forms little more than the outer wall of this cavity. 

 In this plays the trochlear surface of the astragalus. The joint is secured 

 by very strong lateral ligaments, also by a synovial membrane and by an 

 anterior ligament. 



The internal lateral or deltoid ligament {fig. 14 *' ^) arises from the internal 

 malleolus, descends in a radiated manner, and is inserted into the astragalus, 

 navicular, and os calcis. 



The external lateral ligaments are three, a posterior, middle, and anterior. 

 They all arise from the external malleolus, and are inserted into the astra- 

 galus or OS calcis {fig. 14 *■ '). 



The anterior or tibio-tarsal ligatnent arises from the anterior edge of the 

 tibia and tibio-peroneal ligament, and is inserted into the upper and outer 

 part of the astragalus. 



7. Articulation of the Bones of the Tarsus. The seven bones of 

 the tarsus are connected in such a firm and close manner as to admit of little 

 motion between any two except at the articulation between the astragalus 

 and the scaphoid. 



The astragalus is connected with the os calcis by a strong interosseous 

 ligament. There are also two synovial membranes. The head of the 

 astragalus fits into the glenoid surface of the scaphoid, in which it enjoys 

 considerable motion. The S3'novial membrane in the joint is covered 

 superiorly by the superior astragalo-scaphoid ligament. Below is the 

 inferior calceo-scaphoid ligament (fig. 16 ') extending from the anterior 

 inferior part of the os calcis to the lower surface of the scaphoid. ' There 

 is another strong ligament in this joint, called the superior calceo-scaphoid. 

 The inferior and superior calceo-cuboid ligaments {fig. 16 "), as their name 



749 



