THE LIMBS 



181 



phalanges is related to the great development of these 

 bones, and to increasing the mechanical advantage of 

 the flexor tendon which passes over it. Although not 

 present in most mammals, it is not peculiar to the horse, 

 being found, though on a smaller scale, in other Perisso- 

 dactyles. 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 pro- 

 minences with a deep indentation between them, called 

 the c 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 enlargement, the internal 

 framework consists, in addition to the bones, of certain 

 accessory parts — viz., a pair of fibrocartilaginous masses, 

 called the c lateral cartilages,' one attached to each side 

 or wing of the ungual phalanx and extending back- 

 wards towards the heel, and a large elastic fibro-cellular 

 and adipose c 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- 



