TEETH. 



925 



substance (c) which fills the interspaces of the 

 enamelled plates, and here more especially 

 merits the name of " cement," since it binds 

 together the several divisions of the crown 

 before they are fully formed and united by 

 the confluence of their bases into a common 

 body of dentine. As the calcification of each 

 plate begins at the summit, they remain de- 

 tached from each other and like so many se- 

 parate teeth or denticules, until their base is 

 completed, when it becomes blended with the 

 bases of contiguous plates to form the common 

 body of the crown of the complex tooth from 

 which the roots are next developed. 



The plates of the molar teeth of the Si- 

 berian Mammoth (EU-phas prinrigenius) are 

 thinner in proportion to their breadth, and 

 are generally a little expanded at the middle ; 

 and they are more numerous in proportion to 

 the size of the crown than in the existing 

 species of Asiatic Elephant. In the African 

 Elephant, on the other hand, the lamellar 

 divisions of the crown are fewer and thicker, 

 and they expand more uniformly from the 

 margins to the centre, yielding a lozenge-form 

 when cut or worn transversely, as in masti- 

 cation. 



The horizontal as well as vertical course 

 of development of the elephant's grinder 

 is well illustrated by the Mammoth's molar, 

 the last of the lower jaw. The separate 

 digital processes of the posterior plates are 

 still distinct, and adhere only by the re- 

 maining cement ; a little in advance we see 

 them united to form the transverse plate ; 

 and, at the opposite extremity of the tooth, 

 the common base of dentine is exposed by 

 which the plates are finally blended into 

 one individual complex grinder*; this never 

 takes place simultaneously along the whole 

 course of the tooth in the larger molars of 

 the existing Indian elephant, or its extinct 

 congener, the Mammoth. The African ele- 

 phant, and some of the extinct Indian species, 

 as the El. p/anifrons, manifest their affinity 

 to the Mastodon by the basal confluence of 

 the hindmost plates before the foremost ones 

 are worn out. The formation of each grinder 

 begins with the summits of the anterior plate, 

 and the rest are completed in succession ; the 

 tooth is gradually advanced in position as its 

 growth proceeds; and, in the existing Indian 

 elephant, the anterior plates are brought into 

 use before the posterior ones are formed. 

 When the complex molar cuts the gum the 

 cement is first rubbed off the digital summits: 

 then their enamel cap is worn away, and the 



* Some anatomists describe the divisions of the 

 crown of the elephant's grinder as so many " distinct 

 teeth ; " and Mr. Corse (loc. cit. p. 213.), who iirst 

 propounded this view, calls each complex grinder 

 " a case of teeth," and states " that these teeth are 

 merely joined to each other by an intermediate 

 softer substance, acting like a cement." But this 

 description applies only to the imperfectly-formed 

 tooth ; and the detached eminences of the crown of 

 any complex tooth, at that stage of growth when 

 they are held together only by the still uncalcified 

 supporting matrix, might with equal justice be 

 regarded as so many distinct teeth. 



central dentine comes into play with a promi- 

 nent enamel ring ; the digital processes are 

 next ground down to their common uniting 

 base, and a transverse tract of dentine with 

 its wavy border of enamel is exposed ; finally, 

 the transverse plates themselves are abraded 

 to their common base of dentine, and a smooth 

 and polished tract of that substance is pro- 

 duced.* From this basis the roots of the 

 molar are developed, and increase in length 

 to keep the worn crown on the grinding level, 

 until the reproductive force is exhausted. 

 When the whole extent of a grinder has 

 successively come into play, its last part is 

 reduced to a long fang supporting a smooth 

 and polished field of dentine, with, perhaps, 

 a few remnants of the bottom of the enamel 

 folds at its hinder part. When the complex 

 molar has been thus worn down to a uni- 

 form surface it becomes useless as an instru- 

 ment for grinding the coarse vegetable sub- 

 stances on which the elephant subsists ; it is 

 attacked by the absorbent action, and the 

 wasted portion of the molar is finally shed. 



The grinding teeth of the elephant pro- 

 gressively increase in size, and in the number 

 of lamellar divisions, from the first to the last ; 

 and, as the rate of increase in both respects is 

 nearly identical in both jaws, I shall describe 

 them chiefly as they appear in the lower one. 



Thejirst molar, which cuts the gum in the 

 course of the second week after birth, has a 

 sub-compressed crown, nine lines in antero- 

 posterior diameter, divided by three trans- 

 verse clefts into four plates, the third being 

 the broadest, and the tooth here measuring 

 six lines across f ; the first and second plates 

 have two mammilloid summits ; the third and 

 fourth have three or four such ; there is a sin- 

 gle and sometimes a double mammilloid sum- 

 mit at the fore and back part of the crown : 

 the base slightly contracts, and forms a neck 

 as long as the enamelled crown, but of less 

 breadth, and this divides into two, an anterior 

 and posterior, long, sub-cylindrical, diverging, 

 but mutually incurved fangs ; the total length 

 of this tooth is one inch and a half. The 

 corresponding upper molar, which Mr. Corse 

 describes as cutting the gum a little earlier 

 than the lower one, has the anterior single 

 digital process or mammilla, and the pos- 

 terior talon developed into a fifth plate, 

 smaller than the fourth, with which its middle 

 part is confluent ; the neck of this tooth is 

 shorter, and the two fangs are shorter, larger, 

 and more compressed than those of the lower 

 first molar. This tooth is the homologne of 

 the probably deciduous molar (cl. 2) in other 



* In the fossil specimen figured in plate 147, of 

 my " Odontography," the left molar /, exhibits all 

 the above-described gradations of use ; but the right 

 molar, r, through some accident to the opposing 

 tooth in the lower jaw, has not been so worn, 

 but projects beyond the level of the left molar, 

 with the mammillated margins of the plates en- 

 tire. 



j 1 These are also the dimensions of the first lower 

 molar figured by Mr. Corse, loc. cit. pi. vi. ./?<?. l,r>, 

 and./?i/. 3; but I have seen the first lower molar of 

 smaller dimensions. 



