220 Mammalia. 



reached tlie surface. Lastly, underlying the whole series of 

 teeth will be seen the enormous Inferior Dental Nerve, from 

 the dental to near the mental foramen ; and along with it the 

 Inferior Dental branch of the internal maxillary artery (one of 

 the terminal branches of the External Carotid) which sup- 

 plies the teeth. 



IsTow the fact of the three anterior teeth in the body of the 

 jaw having other teeth beneath them, shows them to be 

 deciduous or milk teeth ; and the two next teeth having 

 no such reserve supply, are thereby shown to be two of 

 the true Molar series. But, supposing the internal economy 

 of the jaw were not laid bare, we could still predicate 

 of the three anterior teeth that they were milk teeth ; on 

 this ground, most of the deciduous molars of the Rumi- 

 nantia resemble, in the form of their crowns, the true molars, 

 i.e.f the crowns present throughout a similar complexity; 

 and again, the last milk molar has three lobes like the 

 last true molar (which in this case has not yet cut the 

 gum) ; whereas the premolar permanent series that replace 

 the milk deciduous molars have more simple, or less complex 

 crowns than their predecessors, and are, therefore, less com- 

 plex than the posterior teeth of the series : 



Determination of Age this is of value in ascertaining 

 the age of the beast, for if on examining the jaw the third 

 tooth presents a greater number of lobes than those in advance 

 of it, and all the series look pretty much alike, it is quite 

 certain that none of the premolar series are yet in place. 

 In other words : since 



In the Sheep 



Both anterior and second Premolar appear from the 

 twenty-fourth to the thirtieth month, and the posterior Pre- 

 molar appears from the twenty-seventh to the thirtieth 

 month, it is quite clear that the beast has not attained its 

 second year. 



