PULPS AND SACS OF THE HUMAN TEETH. 49 



antagonism which exists between the median and lateral 

 elements of the intermaxillary system ; and I may now point 

 out, from among the facts formerly detailed, a few instances 

 of the same kind, which must be referred to the same general 

 expression (loi de balancement). 



1. Before the tenth week the upper lip is full and pro- 

 minent, but at that time it begins to recede and gradually to 

 disappear anteriorly, so as to expose the follicles and papillae 

 of the incisive teeth. It afterwards begins to regain its former 

 position and size, and at the fourteenth or fifteenth week it is 

 as large as the inferior, which from the first has not changed 

 its appearance. 



At the tenth week, when the lip begins to recede, the 

 maxillary palate advances its anterior extremity, so as to con- 

 ceal in some degree the intermaxillary palate (median and 

 lateral lobules). When the middle of the lip has disappeared, 

 the maxillary has not only encroached upon the intermaxil- 

 lary, but has also thrown itself into a bundle of irregular folds 

 at its anterior part. As the maxillary palate retires, and the 

 folds become regular crenated rugse, the anterior part of the 

 lip again appears, and at the fifteenth or sixteenth week, it is 

 full and prominent, when the maxillary palate has retired to 

 its proper position. 



2. When the outer lip of the primitive dental groove 

 sends off the laminge, which constitute the greater part of each 

 of the interfollicular septa, and the floor of the secondary 

 groove, the lip itself almost disappears. 



The inner lip, again, which contributes a very small share 

 towards the accomplishment of this process, becomes so much 

 enlarged as to cover the whole groove. 



3. The external and internal lips of the primitive dental 

 groove are, originally, equally prominent. The former, when 

 it sends off the interfollicular septa, diminishes, while the latter 

 increases. When all the follicles of the primitive groove have 



E 



