OSTEOLOGICAL VARIATIONS 103 



garden soil. Similar facts have since been repeatedly 

 observed and noticed. 



In the more internal functions and organs of animals 

 and of plants as well the same variability shows 

 itself. In man himself, as Mantegazza has shown, teeth 

 vary considerably, and a careful study of the third 

 molar tooth has shown that there is a strong tendency 

 towards the disappearance of this part, and while among 

 inferior races all that concerns it is normal in 50 to 54 

 per cent., abnormality becomes considerable among 

 superior races, where the normal state is only met in 

 37*09 per cent., leaving 62'9i abnormal in one way or 

 other. No doubt, we could find numerous cases of 

 variation in the dentition of mammals, although 

 the number and form of teeth is considered as a 

 specific character. But teeth may be considered as 

 external organs in some sense, just as fur or feathers ; 

 and it is even more interesting to see that more 

 internal parts vary perhaps as much, if not more. 

 Such is the case with the bones which go to make 

 the skeleton of mammals and other animals. Some 

 instances are referred to by Darwin, and by Wallace 

 in his recent and valuable Darwinism ; St. George 

 Mivart has shown that the number of ribs varies among 

 the apes ; in man himself the number varies from 

 twelve to thirteen ; and concerning whales, Georges 



