380 Oyt THE FCSdlL BONES OK rACIIYBE-AMATOUS QUADRUPEDS. 



When the two pairs are united, we can observe nothing more than a. 

 large curvilinear square occupying the whole crown of the tooth. 



The two last grinders of the lower jaw have one simple hill more 

 than the others, behind the two pairs of furrowed hills, which form 

 upon the crown, by detrition an oval, placed behind two pairs of 

 trefoil figures. 



The first three sucking grinders have the form of a cone, compressed 

 at the sides, pointed and almost sharp. 



The three replacing grinders succeeding the three last sucking 

 grinders are of a conical form, less compressed, marked with two fur- 

 rows on the external surface, so that detrition gives to their crown a 

 lobed figure. 



Figures 3 and 4 of plate 31 represent the jaws of an hippopotamus al- 

 mostfull grown. Neither in the upper or lower are we able to discover 

 more than the vestiges of the socket of the first sucking tooth, if we 

 may except ?, where a part of that molar still adheres to the upper jaw. 



The points h i, are the two first replacing grinders of the lower 

 jaw, and Z m n those of the upper. 



The third lower tooth, k, is the third sucking tooth wdiich has not as 

 yet fallen, and like the back grinders it exhibits its trefoil figures : 

 but the third upper, n, is a replacing tooth, which has scarcely been 

 worn, as it has only just emerged from the socket, wdiile the first back 

 molar, oand^, is very much worn in both jaws, and already begins 

 to exhibit considerable expansion in its trefoils; they are narrower in 

 the two last molars, as well below, q r, as above, s t ; moreover, the 

 loM'er, q ?', show us the small fang which distinguishes the two last 

 grinders of the lower from those of the upper jaw. 



Such are the appearances in the hippopotamus to the time of its having 

 changed all its teeth. The observations I have made upon the other 

 appearances of that animal have been the result of the examination of 

 seven heads, all of different ages, which admit of our following each 

 tooth throHgh its several successive stages, from the germ when all its 

 hills are unimpaired, and covered with enamel, to the period of its being 

 completely worn down by mastication. 



Hence then we are provided with the means of recognizing the 

 fossil grinders of the hippopotamus, if we should meet wdth them, no 

 matter in what state, or at what age they may have been cast. 



The incisores and the canine teeth are still more easily recognized. 



The lower incisores are directed outwards, as in the pig : they are 

 cylindrical, and become somewhat worn at the point ; their radical part, 

 or that which is contained within the socket, is longitudinally channelled 

 in its periphery. The two middle ones, v v, (figs. 1 and 4, plate 31), 

 are much thicker and four times longer, externally, than the laterals S 5. 



This difference is determined by the position of the upper incisores. 

 They are bent almost vertically downwards, and those on the outside 

 (a, figs. I and 3) are placed much more backvvards than the intermediate 

 teeth, e, so as not to allow the lower laterals, s, to advance in front. 



The upper intermediate teeth are Avorn on their internal surface ; 

 the lateral on their external surface and a little lower : the contrary is 

 the case with the inferior incisores. 



