42 THE MAMMALIA. 



The first indications of teeth are met with at 

 a very early stage of the embryo in the gums that 

 are still in the process of forming, and these be- 

 ginnings of teeth are then gradually enclosed by 

 the gums. In man and most of the other Mam- 

 malia during the first years of life we do not find 

 the whole set of teeth of their later years, of their 

 mature age, nor indeed any such teeth as are to 

 serve them throughout life ; there is at first a 

 temporary set of teeth, the so-called milk teeth. 

 These teeth are very like those that replace them 

 subsequently, the permanent teeth, but are smaller 

 and weaker. It was an extremely interesting and 

 important discovery when Eiitimeyer proved in 

 detail that the milk teeth of many of the Mammalia 

 show a greater agreement with their historical i.e. 

 their geological ancestors than do the permanent 

 teeth. As a rule, for instance, in man the first 

 set of incisors, canine teeth, and front cheek- 

 teeth are replaced by a second set, and thus con- 

 stitute the milk teeth. The teeth which replace the 

 milk cheek-teeth are called premolars, and these 



under the title of Versuch einer Entivickelungsgeschichte des 

 Gebisses (Leipzig, 1882). This work may be recommended as an 

 excellent one on the subject and full of suggestive thoughts, 

 even though we may, at times, feel disposed to dispute some of 

 the views put forward. 



