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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



great majority of instances, the prevailing- number- is seen to be 

 sixteen. 



The last true molar, both in the upper and lower jaws, is subject 

 to a considerable difference of size in different individuals ; but it is 

 readily distinguishable, both by the modification iri the form, and 

 by the circumstance that the ridges constantly either attain or 

 surpass twenty in number. Where the crown is complete, and all the 

 ridges are present, the last upper molar ordinarily presents twenty- 

 four ridges, and the last lower about twenty-seven. The posterior 

 ridges in the ujjper molar are proportionally much less elevated 

 than in the penultimate, the crown in profile, when unworn, pre- 

 senting an outline that is nearly triangular, but prolonged back- 

 wards in the last lower molar ; the posterior ridges, besides being 

 very low, have their apices incurved upon the crown, and they 

 diverge towards their bases somewhat in a fan-shaped manner; 

 while, in the penultimate, the ridges are of a more uniform height 

 from front to. rear, and depart but slightly from parallelism in their 

 general disposition. 



As examples maybe cited the cranial specimen, no. 2662, Cat.Mus. 

 Coll. of Surgeons, which contains the last upper molar, in situ, in fine 

 preservation. On the left side the alveolar wall is removed, to expose 

 the tooth, which has a crown composed of twenty-four ridges, of 

 which only the anterior five are worn. The dimensions are — 



inches. 



Length of crown 13-5 



Height at the sixth ridge 7-1 



"Width of ditto in front, where greatest 3-2 



Another last upper, in a more advanced stage of Avear, and yielding 

 an excellent illustration of this tooth, is presented by the specimen, 

 no. 566 of the Cat. of Foss. Mam. Mus. Coll. of Surgeons. De Blain- 

 ville has given a figure (Osteographie : " Des Elephants," tab. 7. 

 fig. 6) of a deformed last upper molar, composed of about twenty- 

 seven ridges. 



Of the last lower molar in the Indian Elephant a longitudinal 

 section is represented, half the natural size, by fig. 2 of plate 1 of the 

 'Eauna Antiqua Sivalensis.' Tlie entire length of the crown iS' 

 about 15 inches, including in all twentj^-seven ridges, of which the 

 anterior thirteen are more or less abraded. The first five or six 

 ridges incline a little forwards, while the posterior ridges incHne so 

 much in an opposite direction that the hindermost are nearly hori- 

 zontal, producing the flabelliform character that so readily distin- 

 tinguishes, in most instances, the last lower molar from the penulti- 

 mate. De BlainvUle has given, in fig. 6 of plate 9 of his great work, 

 a beautiful representation of a perfect specimen of the same tooth, 

 composed of twenty-seven ridges. Another very fine example of a 

 last lower molar is presented by the specimen, no. 557 of the Cat. of 

 Foss. Mam. Mus. Coll. of Surgeons, there described as being of the 

 Mammoth, but which I regard as being of the existing Indian 

 Elephant, for reasons which will appear in the sequel. The crown 

 is composed of about twenty-seven ridges. In the formula given 



