ELEPHAS PRIMIGENIUS.— TRUE MOLARS. 



125 



plates remain in a space of 7X2| 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 4| inches. The height in front of the 

 molar is 6^ inches. The greatest expansion of the rami at the angle is Yl\ inches, and 

 the maximum thickness of each is 5f inches. The teeth converge, being 3 inches apart 

 in front, 4 inches at the middle, and 1\ inches behind. 



There are fragments of other true molars in the collection from the same locality, 

 shovi^ing thick Widi 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 3'6 X 3'4 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^ 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. Falconer does not seem to have come across a specimen 

 with a lower ridge formula, at all events in the upper jaw, than x 22 x^ 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; 18a- 



x\d X 



X 20 a; 



a? 21 X 



a;22 ar 



x2Z X 



x24 X 



a; 25 a; 



ar 26 a; 



a; 2/ a; 



a; 29 a; 



Upper Molars 



Lower Molars 



4 



1 



5 

 3 



7 

 5 



8 

 1 



4 

 4 



4 

 3 



5 



1 





 03 



2 

 



I 

 



l(?) 



According to the foregoing and numerous other specimens not so entire it appears to 

 me that the ridge formula varies constantl?/ between a? 19 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 , f y. 2 < Pai. Mem.,' ii, p. 1 G8. 



^ 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 



