J28 A MANUAL OF DENTAL ANATOMY. 



As has already been mentioned, there is a well-developed 

 enamel organ with large enamel cells : from these a thin 

 layer of enamel is formed and thus the thin exterior layer 

 upon the teeth of snakes is true enamel, and not, as has 

 been usually supposed, cementum. 



Many points in the development of the teeth of reptiles I 

 have passed over very briefly for the want of space ; a more 

 full account of my observations will be found in the Philo- 

 sophical Transactions for 1875. 



In Mammalia the earliest changes which will ultimately 

 result in the formation of a tooth are traceable at a very 



FIG. 63 



early period ; before the commencement of ossification, the 

 lower jaw consisting solely of Meckel's cartilage imbedded in 

 embryonic tissue, and the lateral processes which become 

 the upper maxillary bones having but just reached as far 

 as the median process which constitutes the intermaxillary 

 bone. That is to say, about the fortieth or forty-fifth day 

 (in the human subject), in the situation corresponding to 

 the future alveolar border, there appears a slight rounded 

 depression, extending the whole length of the jaw, it and 



(*) Embryo at end of fifth week after Carpenter. 1, 2. First two 

 visceral arches, a. Superior maxillary process, t. Tongue. b. Eye. 

 c. Lateral nasofrontal process, nf. Nasofrontal process. 



