Teeth in the Cenletidie. 537 



the niilk-dpntition than in tlic pormanent set. This applies 

 on the whoK> to the same teeth in the h)sver jaw also, as well 

 as to the niilk-preniolars. Moreover, before proceeding to 

 discuss the facts of the case soniewliat more in detail, I would 

 premise, by way of a general observation, that in the Cente- 

 tidaj there is rather less ditl'erence between the accessory and 

 the main cusps ( the former being more, the latter less 

 strongly developed) in the milk- than in the permanent 

 dentition. 



1. Upper Jain. — The least divergence in form between the 

 ]iremolars and molars is found in Echinops^ the premolars 

 of which differ to an extraordinary degree from those of 

 Oryzoryctes hova, which in this respect forms the opposite 

 extreme. The closest approach to Echinops is exhibited 

 by Ericuhis. 



In Echinops and Ericuhis, P. 1 (Hens.) is hardly dis- 

 tinguishable from M. 1 ; the difference from the molars — and 

 from J\d. 1 — to be discussed later on, in the position and 

 height of the antero-external cusp, is demonstrable only in 

 teeth which are intact. In both genera P. 1 is somewhat 

 longer than M. 1, and in Echinops it is also somewhat 

 broader (in the transverse direction) than the premolar of 

 Ericuhis; in the former there is found a low " protocone " 

 and " hypocone." 



In Ericuhis P. 2 already assumes the form of a carnassial ; 

 this is much less the case in Echinops, in which the same 

 tooth is as yet more like a molar, since here the antero- 

 external cusp docs not extend so far forwards, and the whole 

 tooth apjiears altogether less elongate than P. 2 and P.d. 2 

 of Ericu (us (I am not acquainted with P.d. 2 of Echinops). 

 P. 2 of Echinops has in addition a distinct internal cusp 

 (" protocone "), and that of Ericulus has two such cusps likr 

 P. 1 of Echinops. 



P.d oi Echinops resembles a carnassial; but the antero- 

 external cusp is very slightly marked, Three roots are 

 present, and the inner one bears a fairly large internal cusp. 

 The milk-tooth agrees with its successor in iorm. 



In comparison with P. 3 of Echinops, the corresponding 

 tooth in Ericulus is somewhat reduced, and the secodont 

 form begins to be seen : the longitudinal diameter is the 

 greater, while in Echinops the transverse expansion is the 

 more pronounced. There are but two roots. A feebly 

 developed basal margin, as the remains of an internal cusp, 

 is confined to the posterior half of the inner side. A rem- 

 nant of the external cusps, likewise limited to the posterior 

 half of the tooth, is jirosent, as well as in many cases a 



Ann.d) Mag. N. Hist. Ser. 6. Vol. xx. 36 



