16 MICROSCOPIC ANATOMY OF THE TEETH 



while Leche (14) considers that the two laminae are formed 

 simultaneously and independently. 1 



Tooth- The dental lamina or tooth-band with which we are more 

 imme'diately concerned does not pass quite horizontally into 

 the jaw, but is curved, in the maxilla backwards and up- 

 wards, in the mandible backwards and downwards. Little 

 thickenings or buds soon appear upon the dental lamina 

 where teeth are to be formed ; these thickenings, however, 

 do not arise upon the free lower margin of the lamina, but 

 on its labial aspect just short of that margin. The thickened 

 portions grow down into the submucous tissue beneath, 

 forming a cap over the mesodermic dental papilla, and form 

 the enamel organs of the milk teeth (fig. 1). 



In this figure the relations of the mesodermic dentine 

 papilla with the epithelium are shown diagrammatically. 



As the enamel organs are not given off from the free edge 

 of the lamina, there is left a free growing edge above and 

 behind the milk-tooth germs in the upper jaw, below and 

 behind them in the lower jaw, and from this produced 

 portion of the tooth-band the successional permanent teeth 

 are developed. 



These latter then are not produced from the neck of the 

 enamel organ, as was formerly taught, but from the further 

 growing margin of the parent tooth lamina. As the develop- 

 ing jaws continue to grow backwards, the portion of the 

 dental lamina beyond the limits of the forming deciduous 

 teeth is prolonged also in the same direction, and gives rise 

 to the permanent molars. When further developed, the 

 enamel organs become separated from the dental lamina, 

 and are only attached to it by means of connecting bridges 

 which undergo perforation and absorption, the further 

 development of the tooth proceeding independently of the 

 dental lamina. At birth the connecting bands between the 

 milk incisors have nearly disappeared, while those between 

 the first and second temporary molars are still uninterrupted. 



1 For the sake of clearness of description the nomenclature given by 

 Professor Schafer .(Microscopic Anatomy) is adopted. The primitive 

 Zahnleiste is called the primitive dental lamina. The Lippenfurche of 

 Rose is called the labio-dental lamina, and the Zahnleiste of Rose the 

 dental lamina or tooth-band. 



