43 o THE POPULAR SCIENCE MONTHLY. 



speed over the ground or trees, but it is an objection where the limbs 

 are to be used as paddles against the air or water. In fact, the more 

 we know of the skeleton and the environment of the animal, the more 

 we see that its variations throughout the animal kingdom are the com- 

 bined results of the movements of the organism itself and the opposition 

 of the medium in which it moves. Where the actions of the animal are 

 slow, it is found that the bones of the limbs are more rigid and often 

 joined, as shown in the case of the sloth by Prof. Cope. The head and 

 the ends of the limbs, being in constant use against the vital conditions 

 of the environment, are the soonest modified. The bones are formed by 

 the muscles, and the muscles are developed through the movement of the 

 animal. We may all have noticed that, when Ae skin is stripped off, 

 and the extremities of the backbone, the head and tail, are cut off, to- 

 gether with the feet, the carcass of a cat looks much like that of a rab- 

 bit in the same condition. 



Those who have not investigated such an instance of similaritj', yet 

 know that in a butcher's shop there is a superficial sameness in the ap- 

 pearance of meat which it is the business of a good marketer to see 

 through ; while a good many of us, who are unaccustomed to provide, 

 would no doubt be not a little puzzled to distinguish the body of a calf 

 from that of a sheep as it hangs in the stalls. The same thing holds 

 good with the bodies of birds and other animals : a duck is identified 

 most quickly by the webbed feet and flattened bill. Thus it is a matter, 

 perhaps, of general knowledge that an animal is difficult to recognize 

 when the head and extremities of the limbs are missing, and we see now 

 the reason that it is so. We may go even further than this and account 

 for the mistakes of antiquity on the same principle. It is not credible 

 that the head or feet of a mammoth could have been mistaken for those 

 of a man, nor were they as a fact ; but a thigh-bone, or rib, offered less 

 difficulty by reason of the greater resemblance. Hence we find that 

 these mistakes have been made with some excuse for their commission. 

 The difference existing between these fossils and the corresponding 

 bone in man was so small as to escape the notice of the anatomists of 

 antiquity. The general resemblance between the skeletons of all verte- 

 brate animals was not then fully appreciated. People distinguished 

 the animals in old times from man by their heads, feet, and fur, to say 

 nothing of their tails ; and, when they found a*n isolated internal bone, 

 they may readily be forgiven for having wrongly referred it. 



Again, the bones being produced through the muscles, and these 

 through the nutrition of the animal, there is always a proportion be- 

 tween the skeleton and the stomach and soft parts of the body. The 

 skeleton is a very good index of the comparative bulk of the animal, 

 and this fact assists us when we attempt restorations of extinct species. 



From the herd of monkeys found in the Oriental and Ethiopian 

 regions of the Old World, the apes are readily distinguished by certain 

 structural characters. The body is that of a human being, except that 



