THE SKELETON AND LIMBS. 7 



in the loins are commonly seven ; man possesses five, but some animals 

 have as many as nine or as few as two. The sacral vertebree are amal- 

 gamated in most cases into a single bone, and the vertebrae of the tail 

 vary from four to forty-six in number, and are usually freely movable 

 on each other. The number of ribs varies with the number of the dorsal 

 or back vertebrse. 



The limbs are the members in which the greatest differences are seen. 

 The regular number is four, and hence this class, the mammalia, are 

 sometimes called Quadrupeds, or four-footed things. We must remem- 

 ber, however, that many reptiles walk on four legs, and that in some 

 genera of mammalia the hind limbs are either wanting or entirely rudi- 

 mentary. The fore-limbs also exhibit striking differences in the various 

 classes ; the hand in the ape becomes in the cat a paw, and in the horse a 

 single hoof; the fingers in one animal are five in number, in another 

 only one is found. 



This skeleton, this bony framework, is moved by muscles which lie 

 close to the bones and move them in diverse directions. To describe 

 the muscular or other tissues is the function of the anatomists, and who- 

 ever desires to have a perfect knowledge of their wonderful constitution 

 must consult some treatise on Anatomy. Such descriptions are out of 

 place here; it is sufficient for us to remark that the muscles stand in the 

 strictest harmony with the peculiarities of the skeleton and the animal's 

 mode of life, which mode of life both influences and is influenced by the 

 figure of the animal. In some, one muscle is wanting, in others, another ; 

 the whales, for example, have no neck muscles, the apes have them 

 developed as in men. Animals that climb, or burrow, or fly, or prey, 

 have immense muscles to the upper arm ; those that run have immense 

 muscles of the rump and shoulder. In brief, each creature is provided 

 as befits its mode of life, or its mode of life has developed the fitting 

 provision. 



A like variation is seen in the organs of nutrition. The mouth with 

 fleshy, sensitive lips is a characteristic feature of all except the small 

 order of the Monotrcmata. The tcctli vary remarkably both in number 

 and shape. Like the hoof or foot, the teeth are admirably adapted 

 in the case of each species to enable it to support its existence ; and 

 hence these two features form a convenient basis for classification. Teeth 

 indeed are wanting in the scaly and great ant-eaters, and are found in 

 the whale only before it is born, but the great majority of mammals 



