NOT HARE, BUT EASILY LOST. 99 



Remnant teeth are not rare, but it is rare for them 

 to persist in the jaws till even middle age. However, 



preserve even that which, in the altering conditions of life, has 

 become of very little use. Thus we may understand rudimentary 

 teeth to be teeth which are in process of disappearance, having 

 ceased to be useful to their possessors, but still for a time, 

 through the influence of inheritance, lingering upon the scene. 

 Some teeth have disappeared utterly. Thus the upper incisors 

 of ruminants are gone, and no rudiments exist at any stage ; 

 others still remain in a stunted form, and do not persist through- 

 out the lifetime of the animal, as, for instance, the first premo- 

 lars of the horse, or two out of the four premolars of most bears. 



" Teeth are profoundly susceptible of modification, but amid 

 all their varied forms, the evidences of descent from ancestors 

 whose teeth departed less from the typical mammalian dentition 

 are clearly traceable by the existence of rudimentary teeth and 

 other such characters. * * * The power of inheritance is 

 constantly asserting itself by the retention, for a time at least, 

 of parts which have become useless, and by the occasional reap- 

 pearance of characters which have been lost. * * * Things 

 that are rudimentary often teach us most ; for being of no pres- 

 ent use, they are not undergoing that rapid change in adaptation 

 to the animal's habits which may be going on in organs that 

 are actively employed." 



Horses are not the only animals that have had or are having 

 changes in their dentition. Mr. C. R. Darwin says (" Descent of 

 Man," vol. i, p. 25) : " It appears as if the posterior molar or 

 wisdom-teeth were tending to become rudimentary in the more 

 civilized races of men. They are rather smaller than the other 

 teeth. In the Melanian races, on the other hand, the wisdom- 

 teeth are usually furnished with three separate roots, are gen- 

 erally sound, and differ in size from the other molars less than 

 in the Caucasian races. Prof. Schaaffhausen accounts for this 

 difference between the races by 'the posterior dental portion of 

 the jaw being always shortened ' in those that are civilized, and 

 this shortening may, I presume, be safelv attributed to civilized 

 men habitually feeding on soft, cooked food, and thus using 

 their jaws less. I am informed by Mr. Brace that it is becoming 

 quite a common practice in the United States to remove some 



