490 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. 



animals, as in the Ruminants, Pachydermata, etc., does not, 

 according to my observations, exist. 



In animals with successive teeth, as Kolliker (47) has de- 

 monstrated, a process is found, even at the period of the first 

 appearance of the enamel organ at its median side, which is 

 either given off from the neck of the enamel germ or from a 

 still deeper part, and becomes the enamel organ of the per- 

 sistent teeth (see fig. 101). On the other hand, no trace of a 

 dentine germ for these latter teeth is at this period visible. 



Hertz (52) mentions the occurrence in several preparations of a 

 second inflection of the oral epithelium superjacent to the enamel 

 germ of the milk teeth, which he is inclined to regard as the enamel 

 germ of the persistent teeth. Nevertheless there is much here that 

 requires elucidation, especially in respect to the formation of the three 

 molars of man, which, as is well known, are not preceded by milk teeth. 



The processes occurring in second dentition have been very recently 

 minutely investigated by Kehrer (56) and Lieberkiihn (57). As the 

 persistent tooth projects, the alveolar wall dividing it from the milk 

 tooth sacculus undergoes absorption, and with this there immediately 

 occurs a process of cell proliferation in the sacculus of the milk tooth, 

 under the influence of which the fang, with the formation of the so- 

 called Howship's lacunae, is absorbed as far as the crown. The young 

 granulations in the meanwhile take the place of the fang of the milk 

 tooth. The remains of the pulp of the milk tooth unite with the 

 granulations now causing erosion, which, however, are themselves 

 compressed by the growing tooth, that pushes the remains of the 

 milk tooth so far forward that it falls out. No obliteration of the 

 vessels of the milk tooth occur. The true mode in which absorption 

 is effected, the formation of the lacunas of Howship, is no better 

 understood here than in the case of the absorption of bone. Kehrer 

 believes, from finding chalk granules in the protoplasm of young cells, 

 that the amreboid cells of the granulations destroy the dental tissue 

 by a kind of mining process, effected by their pseudopodia. 



The Gubernaculum of the second set of teeth, already described by 

 the older anatomists, consists, according to the observations of Lieber- 

 kiihn, only of a cord of connective tissue, which traverses the alveolus 

 in order to conduct the nerves and bloodvessels to the dental sacculus. 

 It has no relation to the process of dentition itself. 



Our knowledge of the development of simple teeth consisting 



