1870.] 



Mammalian Tooth-dimensions, fyc. 



545 



The respective measurements, which may be taken with a pair of sharp - 

 pointed caliper-compasses, having been pricked out upon the equidistant 

 horizontal lines, the points showing the length and breadth of each tooth 

 are connected by straight lines, and a sort of figure is thus obtained which, 

 in nearly all cases, will be characteristic of the genus or family, and in 

 many instances sufficient to determine the species also. In some cases, 

 as for instance in Canis and Viverra, the odontograms are at first sight so 

 nearly alike that recourse must be had to the pattern of the teeth in addi- 

 tion, as before alluded to. 



In order to render figures of this kind easily comparable inter se, it is 

 necessary that they should be drawn upon some common scale for the 

 distance between the horizonal lines. This is, of course, entirely arbitrary, 

 all that is requisite being that it should not be too great nor too small. 



The accompanying odontograms are drawn upon a scale of '25 inch= 

 6*35 ram., which appears convenient for the purpose ; and is suitable for 

 all teeth of the dimensions that readily admit of this mode of definition, 

 that is to say, which are neither too large, as those of the Elephant, nor 

 too small, as in the smallest mammals. 



Moreover, if the figures are drawn upon ruled paper, the actual measure- 

 ment of the size of the teeth can be read off at sight ; and with this object 

 I have employed paper ruled to a scale of *05 inch. 



The examples selected to show the application of the method above 

 described have necessarily been limited to a very few. They include 

 figures of the dentition of the Lion and Tiger, taken from the largest speci- 

 mens of each species I have as yet met with ; but they afford a fair illus- 

 tration of the way in which even a slight specific difference is brought out, 

 and which, in the case of these animals, is almost confined to the lower teeth. 



The three odontograms of the genus Ursus represent the mean dimen- 

 sions and proportions taken from numerous instances of each species, and 

 they show at a glance the differences between them. In these the small 

 anterior premolars have been purposely omitted to save space. 



The odontograms of Hycena are of the same kind. 



The dentition of the genus Canis is exemplified by instances taken from 

 the Wolf to the Fennec Fox, or from the largest to the smallest species, 

 in order to illustrate the uniformity of the generic type throughout ; and 

 amongst these forms, two will serve to show how the method may be used 

 in palseontological research. Plate IX. fig. 13 represents the dentition of the 

 fossil Fox described by Messrs. Durand and Baker from the Siwalik Hills, 

 and fig. 14 that of the existing Canis bengalensis, which would thus appear 

 to be the close representative of its supposed miocene progenitor, a re- 

 semblance which further comparison of the skulls only serves to render still 

 more obvious. The other figures are introduced merely to indicate the 

 variety of forms produced in this way from the measurements of the teeth 

 of different genera. 



