562 ym. M. p. wooDWAED OK [May 5, 



Inminn ; growing out from this labially ia in both stages a small 

 bud-like mass of cells (fig. 5, du.), in one case swollen at its free 

 end, close to which is a small irregular calcification similar in 

 appearance to the often vestigial do., but smaller in size : this is 

 obviously the vanishing milk-tooth ^., the canine of the adult 

 belouging to the replacing series. 



2'he Premolars. 



In the upper jaw there are three premolars, which Leche 

 believes to be the 2nd, 3rd, and 4th respectively. It is true there 

 is a slight gap between the canine and the anterior of these pre- 

 molars, but there is a more conspicuous one between the two 

 posterior teeth, and in this latter gap the dental lamina has a 

 alight tendency to become specialized and enlarged (Plate XXIIl. 

 fig. b) ; but it is perhaps hardly large enough to be i-egarded as a 

 tooth aniage, and, further, \^'e know that when suppression affects 

 the premolar series in the Placentalia, the 1st tooth of that series 

 generally suffers suppression earliest. 



In the lower jaw there are only two premolars, but between 

 them is a long stretch of dental lamina, which exhibits a most 

 distinct development from its adamantine face ; this growth is 

 slightly indented by a specialized mass of mesoblast (fig. 7 6), the 

 whole structure presenting a great similarity to a developing tooth : 

 this, I beheve, represents the last trace of a suppressed tooth, 

 corresponding with the middle premolar above. 



The two posterior upper, and the posterior lower, premolars 

 are present as functional teeth in both dentitions ; but the middle 

 upper one is very variable, and is often wanting in some adult 

 skulls, while in E. micropus and E. pictiis it is very minute. 



The anterior premolar, above and below, in both my stages, 

 exhibits a large enamel-organ, bell -shaped in the older specimen ; 

 attached to the dental lamina forming the necks of these struc- 

 tures, on the labial side, is in each case a mass of epitheloid cells 

 (figs. 8 and 8 a, dpm. 2) ; the free ends of these buds are swollen 

 and flattened : closely applied to these is, in each case, an irregular 

 calcification, resembling the most reduced stage of ^ ; these are 

 evidently reduced milk-premolars, the anterior functional premolars 

 being then, as Leche supposed, replacing teeth. 



With regard to the last premolar, its milk representative 

 resembles a molar in form, thus differing markedly from its 

 successor ; a feature so characteristic of the 4th premolar of other 

 Placentalia, that I think we may be quite safe in homologizing 

 these two teeth with one another. 



If we examine the mutual relations of the 4th premolar and its 

 successor during their development, we find that the replacing tooth, 

 p pm. 4 , originates almost entirely in front of its supposed milk 

 predecessor from the dental lamina between dpm. 3 and dpm. 4, 

 the enamel-organ of ppm- 4 being more conspicuous in the sections 

 in front and in the anterior region of dpm-J than in its posterior 



