224 



DISSECTION OF THE LEG. 



Open the 

 ankle-joint. 



Synovial 

 sac. 



Surfaces of 

 the bones 

 in the joint. 



Kinds of 

 motion. 



Flexion : 



moving 

 bone : 



state of 

 ligaments. 



Extension 



moving 

 bone ; 



state of 

 ligaments ; 



slight 

 lateral 

 motion. 



Dissection 

 for the 

 joints of 

 the foot. 



Astragalus 

 with os 

 calcis by 



posterior part touch the synovial membrane 1 tetween the astragalus 

 and the os calcis. 



Dissection. Dividing the ligaments of the ankle-joint, separate 

 the astragalus from the bones of the leg, to see the osseous surfaces 

 entering into the joint. 



The synovial membrane of the joint lines the capsule, and is 

 simple in its arrangement; but the cavity is continued upwards 

 for a short distance between the tibia and fibula. 



Articular surfaces. On the tibia there are two articular surfaces, 

 one of which corresponds with the end of the shaft, and the other 

 with the malleolus. On the fibula the surface of the malleolus 

 which is turned to the astragalus is covered with cartilage. 



The astragalus has an upper articular surface, wider before than 

 behind and trochlea-shaped, which is in contact with the end of 

 the tibia; and on its sides are articular impressions for contact 

 Avith the malleoli, of which the outer is the larger. 



Movements. Only the movements of flexion and extension 

 are permitted in the ankle, except slight lateral movement in half 

 extension ; in the former movement the toes are raised towards the 

 fore part of the leg ; and in the latter, they are pointed towards 

 the ground. 



In flexion the astragalus moves backwards so as to project behind ; 

 and the motion is arrested by the wide anterior part of the astragalus 

 being wedged in between the malleoli. 



The posterior ligament is stretched over the projecting astragalus, 

 and the posterior and middle pieces of the external lateral, and the 

 posterior part of the internal lateral ligament, are made tense. 



In extension the astragalus moves forwards over the end of the 

 tibia, and projects anteriorly. A limit to the movement is imposed 

 by the meeting of the astragalus with the tibia behind. 



The lateral ligaments are partly made tight as in flexion, for 

 instance, the anterior piece of the external, and the fore and middle 

 portions of the internal. 



When the joint is half extended, so that the small hinder part 

 of the astragalus is brought into the arch of the leg-bones, a slight 

 movement of the foot inwards and outwards may sometimes be 

 obtained ; but if the foot is forcibly extended, the portions of the 

 lateral ligaments attached to the astragalus prevent this lateral 

 movement by their tightness. 



Dissection. The joints of the foot will be demonstrated by 

 removing from both the dorsum and the sole all the soft parts 

 which have been examined. Between the different tarsal bones 

 bands of ligament extend, which will be defined by removing the 

 areolar tissue from the intervals between them (fig. 87). 



It will be more advantageous for the student to clean all the 

 ligaments before he proceeds to learn any, than to prepare only the 

 bands of one articulation at a time. 



ARTICULATION OF THE ASTRAGALUS AND os CALCIS. These 

 bones form two joints, and are kept together by a strong interosseous 

 ligament ; there are also thin bands on each side and behind. 



