48 ON THE ORIGIN AND DEVELOPMENT OF THE 



and lateral lobules remains the same, and there is no further 

 development of the superior incisives. During the same 

 period the inferior incisives have been rapidly increasing. 



Afterwards the median undergoes much relative trans- 

 verse diminution, while at the same time the laterals acquire 

 a remarkable relative increase, which is accompanied by a 

 corresponding development of the superior incisives ; but the 

 inferiors have now got so much in advance as to retain their 

 advantage ever after. 



On the Laivs which regulate the development of the Pulps 

 and Sacs, and the period of ap>pearance of each of the Tooth- 

 Germs. — In the description which has been given of the earlier 

 phenomena of dentition, it will be perceived that many of 

 them range themselves under the laws recognised by MM. G. 

 St. Hilaire, and Serres — viz. the law of symmetry (loi de sym- 

 metrie), the law of conjunction (loi de conjugaison), the law 

 of balancing or antagonism (le balancement des organes), and 

 the law of eccentric development (loi du developpement 

 excentrique). 



The primitive and secondary dental grooves, the follicles, 

 the cavities of reserve, the osseous alveoli of the milk-teeth 

 and their septa, are all formed originally of tw^o halves, which 

 ultimately join according to the laws of symmetry and con- 

 junction. 



The pidps of the milk-teeth* with their notched laminae 

 are productions from the external lip or ridge of the groove. 

 The interfoUicidar septa, and the osseous alveolar septa, are 

 also developed from without inward (loi du developpement 

 excentrique). 



I have already pointed out the beautiful example of 



* It is a curious fact, that the first tooth-germs which appear — viz. those 

 of the superior anterior and inferior anterior milk-molars — are not productions 

 from the external lip of the dental groove, but bulgings on its floor. 



