MECHANISM OF THE INFERIOR EXTREMITIES. 245 



In extension, the foot is brought with the point downwards, 

 so as to have its upper surface almost on a line with the bones 

 of the leg. The astragalus glides forwards; the tendons, on the 

 back of the joint, are very much relaxed. The joint itself is in 

 a state the reverse of the preceding. 



In the lateral motions, the sole of the foot is caused to pre- 

 sent itself either obliquely inwards or outwards, whereby it 

 may be accommodated to any inclined surface on which we 

 walk. The first position is checked by the internal malleolus, 

 and the tension of the external lateral ligaments; the second, 

 by the external malleolus, and by the tension of the internal 

 lateral ligament. These motions constitute the adduction and 

 the abduction of the foot; and by a regular succession with its 

 flexion and extension, communicate a very limited and embar- 

 rassed species of circumduction. 



The bones of the tarsus, for the most part, have a very ob- 

 scure motion upon each other, with the exception of the arti- 

 culation between the astragalus and the scaphoides, and be- 

 tween the os calcis and cuboides. At these points the move- 

 ment upwards and downwards, makes a sort of flexion and 

 extension of the fore part of the foot, which is very distinct. 

 A species of twisting, or oblique gliding, is also slightly percep- 

 tible there. 



The bones of the metatarsus are susceptible of a slight eleva- 

 tion and depression, which, almost imperceptible at their bases, 

 become sufficiently obvious at their anterior extremities. They 

 also may be slightly approximated, at their fore parts, by the 

 action of muscles, and by external compression. When the 

 weight of the body is thrown upon them, they separate from 

 each other, and the metatarsus loses, in some degree, the arched 

 form of its anterior extremity below. 



The phalanges of the toes have the same motions with those 

 of the fingers, except that they are more restricted. The first 

 ones, therefore, perform flexion, extension, adduction, abduction, 

 and circumdaction ; the last two have only flexion and exten- 

 sion. The extension of the first phalanges is more extensive 



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