36 



DESCRIPTION OF THE PLATES. 



of one side of the lower jaw of the Mas- 

 todon giganteus, \ nat. size ; 1 & 2 are 

 the true deciduous molars ; 3 is their 

 vertical successor or the premolar, (the 

 original was from the upper jaw). 4, 5, 

 d 3, the last of the true deciduous series, 

 which has no vertical successor. Figs. 6 

 & 7 first true molar (fifth tooth deve- 

 loped in succession). Figs. 8 & 9. Se- 

 cond true molar. Figs. 10 & 11. Third 

 or last true molar. The originals of 

 these figures are in the British Museum, 

 and were ohtained by Mr. Koch from 

 newer tertiary deposits in Missouri, North 

 America. Fig. 12, (marked 11 in the 

 plate), a fragment of the upper jaw of 

 the Mastodon angustidens, showing the 

 deciduous molars, and the premolar, ^ nat. 

 size. Fig. 13. Fore part of lower jaw 

 of a young Mastodon giganteus, showing 

 d, i, the deciduous incisive tusks ; d 1, 

 2 & 3, the three deciduous molars, and 

 p 1, outline of their vertical successor 

 hypothetically added. Fig. 14. Fractured 

 fore-part of the lower jaw of adult male 

 Mastodon giganteus, ■§ nat. size, showing 

 i the permanent lower tusk on the right 

 side. From the specimen in the British 

 Museum. Original. 



PLATE 145. 



Fig. 1. Grinding surface of last lower 

 molar, in situ, of the Mastodon latidens. 

 Fig. 2. The same of Mastodon Elephan- 

 toides : both \ nat size. Clift.* Fig. 3. 

 Grinding surface of a lower molar of the 

 Toxodon platensis, nat. size, showing the 

 partial disposition of the enamel e e ; d, is 

 the dentine ; c the cement. Original. 



PLATE 146. 



Fig. 1. Vertical section of the skull of the 

 Indian Elephant with the molars and in- 



* Geological Transactions, Vol. n, 1829. 



cisive tusk of one side, the latter, i, show- 

 ing its alveolus and pulp-cavity exposed 

 by a longitudinal section. The dotted 

 line through the fore-part of the pulp- 

 cavity shows where a ball might pene- 

 trate that cavity and lodge at the opposite 

 side, be there surrounded by osteo-den- 

 tine, then encased in ivory; and by 

 progressive growth of the tusk, be after- 

 wards carried in the direction of the 

 arrow, into the middle of the solid ex- 

 serted part of the tusk. The continua- 

 tion of the dotted line shows how the 

 ball, if it had penetrated the base of 

 the tusk of a young Elephant, might 

 ultimately be discharged. The semi- 

 circular line described round the cen- 

 tral dot in the nasal cavity, gives 

 the curve along which the molars ad- 

 vance in their revolving course from be- 

 hind forwards. Part from Cuvier, part 

 Original. Fig. 2. The penultimate molar 

 and germ of the last molar exposed 

 in the lower jaw of the Asiatic Elephant : 

 a, the bony capsule or alveolus, which 

 moves forwards with the tooth. Fig. 3. 

 Right upper jaw of a very young Ele- 

 phant, fthnat. size. Fig. 4. A detached 

 summit or digital process of a constituent 

 plate of the molar of an Asiatic Elephant, 

 nat. size ; p, the open pulp-cavity at its 

 base. Fig. 5. A detached plate of the 

 same grinder, with a longitudinal section 

 removed from one half, showing d, the 

 dentine, e, the enamel, and c, the ce- 

 ment ; nat. size. Fig. 6. Part of the 

 longitudinal section of an Indian Ele- 

 phant's grinder, showing the interdigita- 

 tion of the constituent tissues ; d, dentine ; 

 e, enamel ; c, cement ; p, is the common 

 pulp-cavity ; r, the beginning of a root. 

 Fig. 7. Part of the longitudinal section 

 of an African Elephant's grinder. Fig. 8. 



