66 PLEISTOCENE MAMMALIA. 



pose, and a minute anterior accessory [d) is added, which, in the milk molar 3 of the same 

 jaw (PI. XIII, figs. 2, 6), becomes an important portion of the tooth. In both these teeth 

 there is in addition an internal projecting " tubercular " cusp (/), the base of which is 

 connected with the summit of [a) by a well marked buttress or rounded ridge, and with 

 the summit of {b) by a similar buttress with a sharper edge. This " tubercle " (/) is 

 represented in the upper incisors by small posterior or internal cusps. We find that in 

 all cases the anterior fang of the tooth, which we will call (a), is concerned in the support 

 of [a) as well as [b) and {d) ; whereas the second outer fang, reckoning backwards, 

 supports the remainder of {a), together with (c) and [e), when they exist; while the re- 

 mainder, whether one or more, &c., support (/), and the cusps serially connected with it. 

 In one-fanged teeth, the relative size of {a) appears to absorb the whole fang (a), the 

 cusps being of perfectly subordinate importance. It may be further remarked, that a 

 has invariably a double cutting edge anterior and posterior to the more or less pointed 

 summit, that the edge of {b) and [c) extend only in the cases where [d) and {e) exist into 

 the clefts which separate these cusps from {b) and (c), but that when either of them 

 terminate the tooth, the edge merges into the more or less rounded anterior or posterior 

 surface. If we apply these rules to the true molar of the lower jaw (PI. XII, figs. 13, 14, 

 15), we shall see that the posterior blade is a shghtly inclined backwards, and that the 

 anterior is {b), being precisely similar in form, though much enlarged, to the same cusp 

 in PM4. 



The only remaining tooth, which offers any modification different to those noticed 

 above, is the small true molar of the upper jaw. The extremely slight definition of the 

 cusps of this tooth, in the genus Felis, would render the determination of them a matter 

 of some difficulty, were it not for the light thrown on their arrangement by other 

 genera. It will be seen, that in the unworn tooth in this genus, there are three minute 

 elevations on the posterior border of the tooth separated from each other by slight de- 

 pressions ; slight ridges from the posterior bases of the two inner cusps, pass round the 

 back of the tooth towards the outer, while a similar ridge is seen to pass round the 

 fore part of the tooth from the summit of the middle to the summit of the outer cusp, 

 on comparing this with that of the corresponding tooth of Canis, say the jackal, we 

 immediately see that these minute elevations represent three well defined and separated 

 cusps in the latter tooth ; the outer cusp is immediately seen to represent {a), the middle 

 one (/), and the inner, a cusp with which we have hitherto not met, which assumes a very 

 considerable development in other genera, and which we call (y.) 



This system of assigning names and letters, and of analysing each tooth, may, perhaps, 

 seem the offspring of fancy ; but we find it to be of great value, both in the accurate 

 determination of the tooth of the Carnivora, and especially in affording a means of exact 

 correlation of the dentition of the recent with the extinct forms, or in other words, of 

 testing, by means of the analysis of the supposed serial development of the teeth, the 

 doctrine of " ordinary succession with modification." 



