150 ZOOLOGY. 



the same number and arrangement of the bones (Fig. 94) as 

 in the human arm. 



290. In mammals organized for speed, the limbs are 

 slender and the feet small ; we see this in the horse, stag, and 

 camel, in which the toes are but little divided (Fig. 95), and 

 the number of the toes is reduced to its minimum ; in the 

 horse, for example, there is but one toe or finger perfect, two 

 others being imperfect and concealed (Fig. 101) ; in others 

 there are two, either alone or with vestiges of one or two 

 others, and these always short and not very moveable. 



In those also remarkable for speed of foot, the limbs are 

 long ; and this is a necessary result of the mechanical prin- 

 ciples already explained. 



Fig. 103. Skeleton of the Kangaroo. 



291. Leaping. In walking, the weight of the body is 

 sustained by a portion of the locomotory apparatus, whilst its 

 centre of gravity is being pushed forward by the other part 

 of the apparatus, so that man never ceases to touch the soil. 

 In leaping it is otherwise ; the body is thrown into the air, 

 and becomes, as it were, a projectile. To effect this, the 

 articulations are strongly flexed, so that, by a strong and 

 forcible and sudden extension, the body may be forced up- 

 wards from the resisting soil. Between the body and the 

 soil there is, in fact, an apparatus representing an elastic 

 spring the joints; on these extending violently and sud- 

 denly one of two things must happen, if the spring be suffi- 

 ciently strong either the soil must yield or the body, and 

 this being generally the only moveable, gives way and becomes 



