ELEPHAS PKIMIGENIUS.—TRUE MOLARS. 
125 
plates remain in a space of 7 X inches. The enamel is thick, as is generally the case in 
the ultimate molars of small individuals as the above must have been. Measured along 
the surface in wear, eight ridges are contained in 4f inches. The height in front of the 
molar is 6g inches. The greatest expansion of the rami at the angle is 17J inches, and 
the maximum thickness of each is 5|- inches. The teeth converge, being 3 inches apart 
in front, 4 inches at the middle, and 7£ inches behind. 
There are fragments of other true molars in the collection from the same locality, 
showing thick and thin enamel. One, evidently portion of a lower last tooth, has decidedly 
thin enamel. Associated with the above is a cuboid and a fourth metatarsal; the former 
is 3 6x3 4 inches, and the latter is 4 inches in length. Teeth of Rhinoceros leptorhinus 
(Owen ?) are preserved also from the same peaty deposit. 
The nearly entire mandible (PI. VIII, fig. 3) described by Davies 1 shows the last 
true molar nearly half worn. The ultimate tooth, for its length and number of 
ridges and the usual tectiform contour of the upper surface, lasts very much longer than 
any of the preceding molars. At all times it represents senility, the degree of which 
becomes excessive when the crown is so ground down that its heel, rising above the level 
of the alveolus, is in front of the anterior border of the coronoid. Then the part of the 
ascending ramus becomes filled by a plug of cancellated bone, which runs up to the 
opening of the dental canal. 
No member of the dental series varies more in the number of ridges than the ultimate 
molar of the Mammoth. Dr. Ealconer does not seem to have come across a specimen 
with a lower ridge formula, at all events in the upper jaw, than x 22 a?, 3 or a higher than 
x 26 x, the prevailing number being x 22 x. Taking all the materials which have come 
under my notice, I find of perfectly entire teeth the following ridge formulae : 
a; 18 a? 
a; 19 a? 
x 20 x 
x 21 x 
x 22 x 
a; 23 a; 
a: 24 a; 
a: 25 a; 
x 26 x 
x 27 x 
a; 29 a; 
Upper Molars ... 
4 
5 
7 
8 
4 
4 
5 
0 
2 
1 
1 (?) 
Lower Molars 
1 
3 
5 
l 
4 
3 
1 
0 3 
0 
0 
According to the foregoing and numerous other specimens not so entire it appears to 
me that the ridge formula varies constantly between xl9 x and x 24 x, so that it is difficult 
to say what is the prevailing number. It may vary possibly between twenty-two or 
twenty-three plates besides talons. Many Arctic molars, like the incisors, attain to very 
large dimensions, and the thinner the plates the greater the number, and vice versa; the 
rule, however, is not absolute. 
1 ‘ Cat. Brady Collection,’ p. 1 1 , ¥ c ¥ . 2 ‘ p a l. Mem.,’ ii, p. 168. 
The higher expressions in lower molars requiring a considerable length of crown would be very 
subject to injury, and this is the case more or less with many of the lower teeth when they attain a 
length beyond 9 to 12 inches. 
17 
