79 



and about half the depth of the breadth. They are composed each of six 

 lobes expanding and continuous at base. The outer and inner pair of lobes 

 are nearly equal ; the intermediate pair is smaller. 



The outer lobes of the molars are conical, and united where contiguous, 

 but they do not form an external buttress by their union, the intervening 

 surface externally being concave. In the last molar the posterior of the outer 

 lobes is proportionately less well developed than in the others. 



The inner lobes of the crown are likewise conical, and united where con- 

 tiguous. The posterior of these lobes is the smaller, and in the last molar is 

 entirely suppressed, or appears only as a slight elevation of the basal ridge 

 occupying the back of the crown. The summit of the antero-internal lobe 

 is prolonged obliquely to join the antero-median lobe. The summit of the 

 postero-internal lobe is prolonged outwardly back of the postero-external 

 lobe, so as to appear as a basal ridge to this part of the crown. 



The median lobes hold a slightly more advanced position than the includ- 

 ing lobes. The back one is isolated or free to its base; the front one, by 

 prolongation, is associated with the antero-internal lobe and the fore part of 

 the base of the antero-external lobe. 



A strong basal ridge occupies the fore part of the crown, and also, less well 

 developed, festoons the outer part. 



In the wearing of the upper molars (Figs. 19 to 21) islets of dentine first 

 appeared at the summits of the six lobes of the crown. Those of the two 

 outer lobes soon became continuous; followed by those of the antero-median 

 and anteror internal lobes With the widening of these two tracts, the islet 

 of the postero-internal lobe next became continuous with that in advance. 

 At this stage there would appear three dentinal tracts: one for the outer pair 

 of lobes, a second for the internal and antero-median lobes, and a third as a 

 circular islet on the postero-median lobe. 



The posterior two premolars (Figs. 19, 21) have bilobed crowns, remind- 

 ing one of the premolars of ruminants. The sudden reduction from the six 

 lobes of the crown of the molars to the single pair of the crown of the pre- 

 molars is a remarkable anatomical character. The lobes are pyramidal, and 

 so far spread apart as to give the crown a greater width transversely. The 

 summit of the inner lobe forms a crescentoid ridge, embracing the bottom of 

 the outer lobe. A strong basal ridge bounds the fore and back part of the 

 crown, and festoons it externally. 



