136 



divided into eighteen plates ; eleven of these have come into use ; the 

 length of the grinding surface being six inches nine lines, its breadth two 

 inches nine lines. Hunterian. 



Structure. 



568. A polished vertical longitudinal section of the superior molar of the 



Mammoth. 



It shows the great depth and number of the descending transverse 

 folds of enamel, and the continuous base of dentine from which the thin 

 lamellar processes arise that are invested by the enamel. The different 

 degrees of density of the three constituent substances, dentine, enamel 

 and cement, are manifested by the different degrees of polish which they 

 have taken. 



From British drift or pleistocene beds. Mus. Parkinson. 



568 1 . A vertical longitudinal section of a corresponding upper molar of an 

 Indian Elephant for comparison with No. 568. The crown of this tooth 

 presents the same complicated interblending of the layers of dentine, 

 enamel and cement ; but the lamellar divisions of the crown, which give 

 rise to that structure, are thicker, shorter and fewer in number. The 

 Mammoth's tooth in an antero-posterior extent of five inches includes 

 twelve plates ; the Elephant's tooth has only ten plates in the same 

 extent. The greater thickness of the softer constituents of the plates, 

 viz. the dentine and cement, in the Elephant's tooth, indicates that the 

 Mammoth, which had a greater proportion of the enamel in its grinders, 

 subsisted on a coarser description of vegetable food than do the existing 

 Elephants of the tropics. 



569. The upper half of a horizontal section of a large inferior grinder of the 



Mammoth, wanting a few of the anterior plates. The cut surface of the 

 tooth, which is eleven inches in antero-posterior diameter, includes fifteen 

 plates, the posterior ones being the thickest. 

 From the drift or pleistocene of Brentford. 



Presented by Sir Jos. Banks, Bart., P.R.S. 



