154 Professor Huxley — On Palceotherium magnum. 



coarse, and the cingulum which surrounds the whole base of the 

 crown is stronger in the adult. 



The patterns of the crowns of the milk molars present the closest 

 resemblance to those of the crowns of the corresponding premolars. 

 The anterior division of the crown of dm^, however, is more nearly 

 straight than that of the crown of jsm*, so that dm^ departs more from 

 the bicrescentic pattern than pm^ does. The sharp backwardly 

 directed ridge (Plate VI., Fig. A, a) upon the outer face of the an- 

 terior division of this tooth, which takes the place of the rounded 

 and convex surface of the anterior crescent of the other teeth, appears 

 to be somewhat more marked in the milk than in the permanent 

 tooth. I can discern no differences of more than individual value 

 between the other milk teeth and those permanent teeth which 

 replace them. 



In the adult dentition, the hindermost molar has, as in all other 

 Palasotherian mammals, a strong posterior lobe, with a convex outer 

 and concave inner aspect. It is 0-7in. long, or nearly a third as long 

 as the whole crown, which measures 2-2in. 



The milk dentition of the Khinoceroses and of the Horses is, at one 

 period, in a condition which exactly corresponds with that of 

 Palceotherium magnum. That is to say, the three posterior milk molars, 

 dm^, drn^, dm''', are in place and ready for use, while dm^ remains in 

 its alveolus, and is only cut very much later. 



The foal differs from the young PalcBotherium in the length of the 

 crown of dm^, which is as great as, if not greater than, that of the 

 crowns of the other two milk molars ; in the greater distance of 

 the alveolus of dm^ from dm^, and in the much greater length of the 

 diastema. 



In the Ehinoceroses on the other hand(e.g. Mh. indicus) dm^ is smaller 

 in proportion to dm^ than in the PalcBotJierium, and, if there were a 

 canine tooth, the diastema would be as short as in the latter. 



In the form of the ramus the Horse lies between the Palaeoiherium 

 and the Ehinoceros. 



It follows, from what has been stated, the rule which has been laid 

 down for the Ungulata in general, that the crown of the last milk 

 molar in the lower jaw always remembles that of the last true molar, 

 does not hold good for Palceotherium. The genus Paloplotherium was 

 founded upon the supposition that it did, and Pictet in the following 

 passage very properly bases the distinctness of Paloplotherium from 

 Plagiolophus, only on the ground that Paloplotherium is asserted to 

 have no third lobe to its posterior lower molar. 



II resulte de la : — 1. Que le P. minus et le P. annectens se ressem- 

 blent par tout I'ensemble de leur dentition, et qu'ils different par 

 phisieurs points essentiels des vrais Palceotherium. 



2. Qu'ils se distinguent cependant I'un de I'autre pai' la forme de 

 la derniere molaire inferieure, que est a trois collines dans le 

 premier et a deux dans le dernier. 



3. Que le P. annectens doit en consequence former un sous genre 

 special qui conserverait le nom de Paloplotherium, donne par M. 

 Owen, et que le P. minus est le type d'un autre sous genre tres 



