NATURAL THEOLOGY. 269 



pasture ; because such a substance upon the fore- 

 head of the young animal would very much in- 

 commode the teat of the dam in the office of 

 giving suck. 



But in the case of the teetJi — of the human 

 teeth at least, the prospective contrivance looks 

 still farther. A succession of crops is provided, 

 and provided from the beginning ; a second tier 

 being originally formed beneath the first, which do 

 not come into use till several years afterwards. 

 And this double or suppletory provision meets a 

 difficulty in the mechanism of the mouth, which 

 would have appeared almost insurmountable. 

 The expansion of the jaw (the consequence of the 

 proportionable growth of the animal, and of its 

 skull) necessarily separates the teeth of the first 

 set, however compactly disposed, to a distance from 

 one another, which would be very inconvenient. 

 In due time, therefore, i. e., when the jaw has at- 

 tained a great part of its dimensions, a new set of 

 teeth springs up, (loosening and pushing out the old 

 ones before them,) more exactly fitted to the space 

 w-hich they are to .occupy, and rising also in such 

 close ranks, as to allow for any extension of line 

 which the subsequent enlargement of the head 

 may occasion.^^ 



62 The second or permanent set of teeth does not push out the 

 deciduous or milk teeth. The process is not mechanical. Whilst 

 yet a tender membrane is around the second tooth, those of the 

 first set are suffering absorption at their fangs. Another circum- 

 stance, which shows the provision not to be mechanical, is the 



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