70 ODONTOGRAPHY. 



very perfect specimens of those in the lower jaw : by the aid of these, and 

 a comparison of the alveoli, we may presume that these two teeth in the 

 upper resembled the corresponding teeth in the lower jaw. 

 Third The third deciduous molar has also never been described ; and, as we 



Tooth. 



have it in place in at least half a dozen instances, we shall be able to give 

 a description of it. This tooth is larger than the two .preceding, having 

 three instead of two ridges, — those being bi-lobate, and this tri-lobate ; 

 thus resembling the second milk molar of the Mastodon Longirostris, and 

 differing from the corresponding tooth in that species, because the latter has 

 four lobes. Being always the tooth of a young animal, it is small ; in this 

 specimen, two inches and a half in length, by two inches in breadth. (See 

 Plate TV., where this tooth is represented in place.) It has, as already 

 said, three ridges, each of which is partially divided into two principal 

 tubercles ; but, being rather serrated than notched, it presents four small 

 tubercles. These are moderately worn, but not so much as those in the 

 corresponding tooth of the lower jaw. The basal cingulum is more promi- 

 nent on the outer than on the inner edge. The roots are firmly imbedded 

 in their sockets. ■ 

 Fourth The fourth, upper, and first permanent molar has also three ridges, 



like the last deciduous. It is smaller than the corresponding tooth of the 

 lower jaw, represented Plates III. and V., which belonged to a much older 

 animal, but larger than the preceding tooth. It measures three inches in 

 length, two inches and a half in breadth. The mammillary eminences are 

 more distinctly notched than in the preceding tooth, being less worn. The 

 basal cingulum is rather more prominent on the outer than on the inner 

 edge of the tooth. In another head of much greater size, belonging to the 

 University at Cambridge, the dimensions are larger. 



Tooth. 



