61 



wide anterior l)asal ridge of the crown. In tlic last molar the jiosterior of 

 the outer lol>cs is proportionately less well developed than in the molars in 

 advance. The inner lobes of the crown are conical internally, and are extended 

 obliquely outward so as to form ridges continuous with the fore part of the 

 outer lobes. The oblique valley separating the inner lobes is closed exter- 

 nally by the conjunction of the outer lobes. A wide, angular recess occupies 

 the interval of the posterior lobes of the crown and the posterior basal ridge. 



In the unworn or moderately worn condition of the molars, as seen in Fig. 11, 

 Plate IV, a narrow but conspicuous ridge or fold is observed projecting from 

 the antero-external lobe into the median valley of the ci-own. In the 

 worn condition of the molars, as seen in Fig. 10, c to g, they exhibit a 

 Iract of exposed dentine extending along the summits of the outer lol)es 

 including the abutment in front, and prolonged inw^ardly in two pouch-like 

 extensions upon the summits of the inner lobes. 



The upper premolars not only exhibit from behind forward a successive 

 diminution in size, but also a reduction to greater simplicity. The latter con- 

 dition is induced through connation and disappearance of constituent elements 

 as they are observed to exist in the back teeth. Thus if we compare the 

 back two premolars, Fig. 10, c, d, with the molars behind, it will appear tliat 

 the most striking difference is due to the connation internally of the inner 

 lobes. From this arrangement the premolars appear to have a single loi>e to 

 the inner part of the crown, from which a pair of ridges proceed to join the 

 outer lobes. A central pit represents the median valley opening internally in 

 the crown of the molars. The basal ridge extends around the inner part of 

 the crown. 



The abutment so conspicuous at the antero-external angle of Ihc crown of 

 the molars is successively reduced forward in the premolars and disappears in 

 the anterior two. 



In the crown of the second premolar. Fig. 10, h, the outer lol^es are more 

 connate than in those behind, and the inner lobe appears more isolated from 

 the absence of the intervening ridges. 



The crown of the first premolar, Fig. 10, a, about half the size of^that of 

 the tooth behind, is conoidal with an oval base. For the most part it is 

 homologous with the outer lobes of the other premolars in a completely con- 

 nate condition. A small offset internally is a ruiliment of llie inner lobe of 

 Ihe succeeding premolar. 



