52 ANIMAL LIFE 



body is carried clear of the ground and supported 

 mainly on the straight fore-limbs, whilst propulsion is 

 effected by the more bent hind-limbs, which are straight- 

 ened by very powerful muscles and tendons; and to 

 provide a sufficiently firm point d'appui for these the 

 hip-girdle and vertebrae of the small of the back are 

 greatly enlarged. To give them additional leverage 

 the bones of the shank and foot are elongated. To 

 ensure elasticity of tread, fleshy pads are developed in 

 carnivores under the middle joint of the toes, and in 

 cats the claw-bearing ones are held back in walking 

 by means of a tendon in a protecting sheath, and only 

 dart out by the action of prehensile muscles. For 

 support on slippery ground the heel is raised still 

 higher than in carnivores, and only the end joint of 

 the toe converted into a horny hoof. Among these 

 mammals, the so-called Ungulates, a remarkable reduc- 

 tion in the number of toes has taken place. Instead 

 of the five which only elephants have retained, rumi- 

 nants have only two the third and fourth ; pigs 

 and rhinoceros four, peccaries three, and horses one. 

 The cloven hoof, characteristic of those that chew the 

 cud, alone touches the ground, but traces of the 

 second and fifth toes are seen in the deer, and are of 

 use in spreading out the animal's weight when soft 

 ground is encountered. 



Of the many special modes of motion adopted by 

 mammals only a few can be mentioned. 



In monkeys and apes the habit of climbing and 

 of sitting nearly erect throws the weight of the body 



