544 Prof. G. Busk on Graphic Representation of [June 16, 



X. u On a Method of graphically representing the Dimensions and 

 Proportions of the Teeth of Mammals." By George Busk, 

 F.R.S. Received May 20, 1870. 



Of all the hard parts of animals, the teeth, more especially for palseonto- 

 logical purposes, undoubtedly afford the most constant and the most gene- 

 rally available characters. Any plan, therefore, by which the study and 

 ready comparison of these organs may be facilitated and simplified cannot 

 fail to be of some use to the zoologist and palaeontologist. 



Having myself found the method I am about to describe convenient in 

 many instances, more particularly in the case of fossil mammals, I have 

 been led to believe, by the representations of several to whom it has been 

 communicated, that it might be found useful by others, and consequently, 

 though at first sight but a trifling matter, worthy of a place in the * Pro- 

 ceedings ' of the Society. 



The characters afforded by the teeth are derived from their number, 

 proportions (absolute and relative), and pattern. 



In many cases the pattern of the teeth must undoubtedly be taken 

 into account ; but in a very great number it will be found that the 

 number and proportions, more particularly of the premolars and molars, 

 are sufficient for the purpose of diagnosis, or, at any rate, that a knowledge 

 of these particulars alone will reduce the necessity for further comparison 

 within a small compass. A good illustration of this is afforded in the 

 smaller Felidse, in which, owing to their high specialization, the pattern of 

 the teeth is in the main so very closely alike as to render it of very little 

 assistance in diagnosis, though not altogether. 



The statement of the particulars above mentioned, in words or figures 

 when numerous comparisons are needed, is tedious and laborious to both 

 writer and reader ; and even in the most carefully arranged tables it is 

 difficult without close attention to perceive at once differences which 

 though minute are, from their constancy, important and in fact necessary 

 for the diagnosis of nearly allied forms. 



My plan may be termed one for the graphic or diagrammatic represen- 

 tation of the absolute and relative or proportional dimensions and number 

 of the premolar and molar teeth, or of those constituting the molar series, 

 and which have appeared to me in most cases sufficient for the purpose in 

 view. But of course the incisors and canines might be included in the 

 scheme if thought requisite. 



The method in which these "odontograms" are prepared will be at once 

 obvious on inspection of the accompanying examples. Each horizontal line 

 in the figures, which represent the maxillary and mandibular molar series 

 of a species, corresponds to a single tooth, whose extreme length or an- 

 teroposterior diameter is indicated by the extent of the lighter shade, and 

 its extreme breadth or transverse diameter by the darker shade. Both 

 dimensions are, of course, measured from the same base-line. 



