44 ON THE ORIGIN AND DEVELOPMENT OF THE 



however, is short in its duration, and simple in its details, it 

 may be included in the first stage. 



The first or follicular stage comprehends all the phenomena 

 which present themselves from the first appearance of the 

 dental groove and papillas till the latter become completely 

 hid by the closure of the mouths of their follicles, and of the 

 groove itself. It is upon this hitherto unknown stage of 

 dentition that I have insisted so much in the former sections 

 of this paper. 



The second or saccular stage is the one with which ana- 

 tomists have been so long familiar, during which the papillae 

 are pulps, and the open follicles which contain them are shut 

 sacs, when the tooth-substance and the enamel, constituting 

 the teeth themselves, are deposited. It is during this stage, 

 also, that some of tlie most interesting phenomena in the 

 formation of the alveolar processes present themselves. 



The third or eruptive stage includes the completion of the 

 teeth, the eruption and shedding of the temporary set, the 

 eruption of the permanent, and the necessary changes in the 

 alveolar processes. 



When viewed in reference to an individual tooth, these 

 three stages are distinct ; but when viewed in reference to 

 both sets, and to the whole process of dentition, they become 

 somewhat intermingled. 



When considered in the latter point of view, we may state 

 that the follicular stage commences at the sixth or seventh 

 week, and terminates at the fourth or fifth month of intra- 

 uterine existence ; that the saccular commences at the ter- 

 mination of the first, and lasts for certain of the teeth till the 

 sixth or eighth month, and for others till the twentieth or 

 twenty-fifth year of extra-uterine existence; and that the third 

 or eruptive commences at the sixth or eighth month, and lasts 

 till the twentieth or twenty-fifth year. 



