150 



Hereupon it may first be observed, with regard to the specimens 

 Nos. 612 and 613, that the continuous undulating line of enamel exists 

 only at that part of the crown which is worn down to the common 

 dentinal base, and that this is first exposed along the middle tract of the 

 grinding surface in consequence of the greater depth of the transverse 

 fissures at the margins than at the middle of the coronal plates. Se- 

 condly, it follows from the structure of the molars Nos. 562 and 563, 

 that the coronal plates would not necessarily become detached after de- 

 composition of the cement in the completely-formed grinders of either 

 the ordinary Mammoth or existing Elephants : the idea of the separation 

 of the coronal plates, as a necessary consequence of decomposition of 

 the cement, could be entertained only on the view of the grinder being- 

 composed of a number of denticules attached together by the cement 

 alone. Such separation, however, takes place only in incompletely deve- 

 loped molar teeth, the lamelliform divisions of the crown being held 

 together independently of the cement as soon as the calcification of the 

 dentinal pulp has completed their uniting base. 



Without this knowledge of the mode of development of these complex 

 teeth, of the essential nature of the coronal plates, and their liability to 

 varying inflections, the appearances upon the grinding surface, which are 

 actually due to such variations and to dirferent degrees of attrition, might 

 be viewed as characters of distinct species of Mammoth. 



614. The lower molar of a Mammoth: the grinding surface of the crown is 



seven inches in extent, and displays the summits of eighteen transverse 

 plates ; the first and second of which have been worn away to their com- 

 mon dentinal base : the penultimate plate displays four detached rnam- 

 millary processes, and the two next plates in advance show four dilatations 

 with alternate constrictions. This is a good example of the thin-plated 

 variety of the Mammoth's grinder. 



Locality unrecorded. Mus. Parkinson. 



615. The right upper molar of a Mammoth, twelve inches in length, and with 

 the crown divided into twenty-six transverse plates : the summits of 

 seventeen of these are exposed upon the grinding surface of the crown, 



