THE LIMBS. 193 



smaller scale, in other Perissodactyles. Not only is 

 the ungual phalanx larger, or at all events broader 

 in proportion to the rest of the digit, than in any 

 other mammal, but the parts around it are increased 

 to a still greater ratio, in order to give that firm basis 

 of support necessary when only a single toe reaches 

 the ground. In addition to its breadth, the toe is 

 prolonged backwards on each side into rounded 

 prominences with a deep indentation between them, 

 called the " heels " of the foot, as in comparing the 

 toe of the horse to the entire human foot they occupy 

 much the same position as the heel of the latter, 

 though, of course, they are in reality totally different 

 parts. In order to provide a support for this enlarge- 

 ment, the internal framework consists, in addition to 

 the bones, of certain accessory parts — viz., a. pair of 

 fibro- cartilaginous masses, called the "lateral carti- 

 lages," one attached to each side or wing of the un- 

 gual phalanx and extending backwards towards the 

 heel, and a large elastic fibro-cellular and adipose 

 "plantar cushion" (Fig. 25, 17), occupying all the 

 median region below and behind the bone. The 

 former have nothing corresponding to them in man, 

 but the latter agrees in position and structure to the 

 fibro-fatty cushion of the bulb at the end of the hu- 

 man finger (Fig. 24, 17). 



In the horse this " plantar cushion " is of great 



