The deciduous formula, is :—
incisors — ; molars— : — 16.
226. Mastodon gigant'eus.—I shall first describe the molar teeth in
the Mastodon giganteus, as these best exhibit the tapiroid character of the
grinding surface. This character is most strongly manifested, agreeably
with the law which has been so frequently illustrated in the present
work, by the molars which are first developed in the young animal, at
the period of dentition when it has receded least from the common
type. The crown of the first deciduous molar in the lower jaw
(PI. 144, fig. 1, d 1) is subquadrate, one inch four and a half lines
in antero-posterior diameter, one inch three lines across its broadest
part; it supports two transverse ridges, the anterior one most deeply
cleft into two mastoid eminences, the posterior and broader ridge
having one angle produced forwards: the front, back and outer
part of the bases are girt by a tuberculate ridge; the whole is supported
by two long subcompressed divergent fangs. (1)
The second deciduous molar (PI. 144, fig. 2, d 2) has a crown,
like the first in shape, but measuring one inch eleven lines, by
one inch eight lines, and having both transverse ridges subdivided
into two mastoid eminences, and a larger posterior basal ridge;
it is supported by two fangs. (2) It is displaced and succeeded vertically
by a tooth (ib. fig. 3, p 1) of a more simple form, having
a crown broader in proportion to its length, supporting two bifid
transverse ridges, and girt by a basal cingulum ; it measures one
inch five lines by one inch four lines. This tooth may be regarded
as the first of the theoretically permanent or adult series of teeth :
it answers to the penultimate premolar in the Dinothere and Tapir,
but is very soon shed.
The tooth (ib. figs. 4 & 5, d 3) which answers to the last
milk molar in the above cited Pachyderms, rises into place and
use, as in these and other Quadrupeds, before the premolar is
developed: its; crown supports three bifid transverse eminences,
(1) On this tooth is founded the nominal species Mastodon tapiroides of Koch and
Grant. Geol. Proceedings, vol. h i, p. 771. It is figured on the left side of the lower jaw
of the young Mastodon referred by Godman to the Tetracaulodon, loc. cit. PI. 18.
(2) This tooth is also figured in the Plate above cited of Dr. Godman’s Memoir.
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 posterior
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 complexity,
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, (PI. 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 posterior
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, subdivided
into three or more roots.(3)
(1) The lower jaw of the Mastodon giganteus 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 (e) 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 deciduous
tusks j 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.