MASTODON. 617 



and a tuberculate ridge along the front, back and outer part of 

 its base: specimens vary in antero-posterior diameter from two 

 inches ten lines, to three inches three lines in length ; the tooth 

 here figured was two inches four lines across the broadest pos- 

 terior lobe. The crown is supported by two small anterior fangs 

 and one large posterior root. This tooth ought, theoretically, to 

 be succeeded and displaced vertically by a premolar, answering to 

 the last in the Tapir ; but the rapidity of the horizontal progress of 

 the true molars, and their progressive increase of size and com- 

 plexity, appear to be the conditions of the interrupted development 

 of the premolar series, and which operate to their entire suppression 

 in the genus Elephas. 



The antepenultimate or first true molar, the fifth of the series 

 developed in succession, (PL 144, fig. 6 & 7, m 1) resembles the 

 preceding in conformation, but is larger, and the basal ridge is 

 commonly less distinct on the outer side : its antero-posterior 

 diameter is four inches one or two lines, its breadth which is 

 more equable than in d 3, is three inches. (2) In the young 

 tooth figured, the marks of the subdivision of the eminences of 

 the primary mastoid lobes are not obliterated. 



The penultimate, or second true molar, the sixth of the series 

 in succession, (ib. fig. 8 & 9, m 2) has also the crown divided into 

 three transverse eminences, each cleft down the middle, but the pos- 

 terior basal ridge is usually more developed. The antero-posterior 

 diameter of the crown is from five inches to five and two thirds ; 

 its transverse diameter three inches and a half to three and two- 

 thirds. The first transverse eminence is supported by a single 

 fang, the remainder of the tooth by a broad thick base, sub- 

 divided into three or more roots. (3) 



(1) The lower jaw of the Mastodon giyanteus figured by Dr. Hays, Transactions of the 

 American Philosophical Society, Vol. iv, 1831, PI. 20, shows the stage of dentition when the 

 two true deciduous molars have been shed, the first true molar (c) in place, and before the first 

 premolar (if this tooth be developed in the lower as in the upper jaw) had risen. The fractured 

 state of the symphysis prevented the recognition of the remains of the alveoli of the deci- 

 duous tusks ; the specimen being most probably of a young female Mastodon. 



(2) A portion of this tooth is figured by Dr. Hays, loc. cit. PI. 20, fig. 1, d. 



(3) This tooth is figured by Dr. Hays, loc. cit. PI. 21, e,, and by Cuvier, 'Ossemens 

 Fossiles' tom. i. Grand Mastodonte, PI. 1, fig. 5. 



