58 ANIMAL MECHANICS 



This arch of the foot, from the heel to the toe, 

 has the astragalus (A) resembling the keystone 

 of an arch ; but, instead of being fixed, as in 

 masonry, it plays freely betwixt two bones, and 

 from these two bones, B and C, a strong elastic 



ligament is ex- 

 tended, on which 

 the bone (A) rests, 

 sinking or rising as 

 the weight of the 



body bears upon it, or is taken off, and this it is 

 enabled to do by the action of the ligament which 

 runs under it. 



This is the same elastic ligament which runs 

 extensively along the back of the horse's hind 

 leg and foot, and gives the fine spring to it, but 

 which is sometimes ruptured by the exertion of 

 the animal in a leap, producing irrecoverable 

 lameness. 



Having understood that the arch of the foot is 

 perfect from the heel to the toe, we have next to 

 observe, that there is an arch from side to side ; 

 for when a transverse section is made of the bones 

 of the foot, the exposed surface presents a perfect 

 arch of wedges, regularly formed like the stones 

 of an arch in masonry. If we look down upon 

 the bones of the foot, we shah 1 see that they form 

 a complete circle horizontally, leaving a space in 

 their centre. These bones thus form three dif- 



