244 SKELETON. 



In extension, the patella rises upon the condyles, and becomes 

 prominent; the lateral ligaments are rendered somewhat tense, 

 and the motion is finally checked, by the resistance of the cru- 

 cial and of the posterior ligaments of the articulation. 



The rotation of the bones of the leg can only be performed 

 when they are flexed, and the ligaments, generally, thereby re- 

 laxed, in which position a very limited motion, inwards and 

 outwards, is perceptible. The motion, outwards, is the more 

 extensive of the two, in consequence of the arrangement of the 

 crucial ligaments, which are separated from each other by it. 

 The motion, inwards, is limited by these ligaments being 

 brought immediately by it into close and resisting contact with 

 each other. In either case, however, the posterior and the la- 

 teral ligaments all contribute, ultimately, to arrest the motion. 



In all these conditions of the leg, the semi-lunar cartilages 

 slide somewhat upon the head of the tibia. 



The articulation between the tibia and the fibula is such as 

 to admit of no motion whatever below; but, above, a limited 

 sliding backwards and forwards is performed by the fibula 

 upon the tibia. This movement is made more perceptible in 

 cases of extreme emaciation, and in general relaxation of the 

 muscular system. 



3. Of the Motions of the Foot. 



The general motions of the foot upon the bones of the leg 

 are flexion, extension, and an inconsiderable inclination inwards 

 and outwards. 



In flexion, the astragalus rolls backwards in the articular 

 cavity formed by the tibia and the fibula, and is arrested by the 

 anterior upper part of the astragalus coming in contact with 

 the articular margin of the tibia. The ligamentous fibres and 

 the synovial membrane, in front of the articulation, are re- 

 laxed; those behind are in a state of tension, as well as the 

 tendo-achillis, and the other tendons there. Luxation from an 

 excess of this motion is impossible. 



