Parr.] 1^2 [May 15, 



from the other teeth, while the simple character of Pm. 1 has already 

 been sufficiently commented upon. The last lower molar, as in so 

 many forms, diflers from the others in the presence of an additional 

 less well-developed lobe situated posteriorly. The lower molars and 

 Puis. 3 and 4 have oblono-, quadrate crowns, with an outer pair of fore 

 and aft principal lobes, and an inner pair of secondary lobes connate 

 with them. "The principal lobes of the crown are slightly oblique in 

 their relative position, angularly convex and sloping externally, con- 

 cavely excavated internally and are acutely crescentoid at their summit. 

 Of the inner secondary lobes, the anterior is much the larger, and is 

 pyramidal in form with a twin pointed summit." This character is 

 observable only in teeth that are not worn excessively and disappears as 

 the summits of the crown are worn off in mastication. "The antero- 

 internal cusp springs from the crown at the conjunction of the principal 

 lobes and is continuous with their contiguous crowns. The posterior of 

 the secondary lobes is conical and springs from the crown in conjunc- 

 tion with the back horn of the posterior principal lobe. The front horn 

 of the anterior principal lobe curves inward, downward and backward 

 to the base internally of the anterior secondary lobe. A basal ridge (or 

 cingulum) nearly continuous bounds the crowns of the lower molars 

 externally. Posteriorly it rises inward and terminates in a tubercle 

 springing from the conjunction of the two posterior lobes." Pm. 2 

 deserves a slight mention in passing. In the lower jaw the posterior 

 half of this tooth is an exact copy of the corresponding part of any of 

 the succeeding premolars or molars. One half of the antero-interual 

 lobe is present as usual, but this alone forms all of what corresponds to 

 this lobe in the succeeding teeth. Anterior to this and externally there 

 is another lobe more nearly median in position. This is connected with 

 the former by a ridge and the two together form a lobe which is very dif- 

 ferent from any of the others. Anterior to this and connate with it is a 

 small lobe on the internal surface of the tooth. The deciduous tooth 

 differs from the permanent one in that in the former the two anterior 

 lobes are more distinct from each other and from the other lobes, so that 

 we seem to have five lobes in this tooth. Again in the earlier set this 

 tooth has a greater antero-posterior extent than any of the other teeth, 

 almost equaling in length M. 3 of the permanent set, which has the 

 additional lobe. In the permanent set Pm. 2 is even shorter antero-pos- 

 teriorly than the succeeding tooth in the premolar series. In the milk 

 set D. 4 has the posterior half narrower than the anterior half. In D. 3 

 both halves of tooth are of approximately the same width, while, in the 

 permanent premolar series the posterior half of the tooth is always the 

 wider, while in the molar series the reverse condition obtains. The cin- 

 gulum is not so well developed on the deciduous molars as on the corre- 

 sponding teeth of the permanent set. It is not developed on the external 

 surface of the posterior lobe as in the permanent tooth, but is present on 

 the posterior border of tooth where it ends in a tubercle. The cingulum 



