114 



do not otfer any feature of moment until m^ is reached. This tooth — 

 normally the last of the series — has approximately the normal form ; 

 and the "pattern" on its wearing surface is also apparently that of 

 the normal last tooth. But it should be remarked that some of the 

 tooth has been broken away (Fig. 1, *) thus giving rise to some 

 difficulty in determining the exact "pattern", and also in making the 

 measurements to be referred to later. The position of the tooth in 

 the jaw is abormal inasmuch as the extra tooth (m') has caused it 

 to be rotated so that its posterior end points inwards to some extent, 

 and the whole tooth slopes forwards. The supernumerary tooth on the 

 right side is imperfectly developed, but not markedly so. Its inner 

 and outer surfaces are unusually well ridged, this being especially so 

 on the inner surface. The tooth projects considerably above the 

 general level of the cheek-teeth, evidently because it has not had to 

 withstand so much wear as the other teeth. As a consequence the 

 wearing surface is not provided with a well marked "pattern". It 

 should be noticed (Fig. 1) that the position of this tooth in the jaw 

 is that of a normal tooth; that is, its long axis coincides with the 

 long axis of the mandible. This is of some interest because the same 

 circumstance is to be observed in the other specimen and also in the 

 illustration given by Hayes. 



On the left side, as on the right, the teeth are normal as far 

 as m^, which like its opposite fellow has the form of a normal last 

 tooth, but is rotated by the pressure of the supernumerary molar so 

 that its narrow posterior end points towards the mesial plane. The 

 additional molar (m'*) is better developed on the left than on the right 

 side ; and it closely approximates a normal last tooth, both in form 

 and "pattern". Like the corresponding tooth on the other side of the 

 jaw, it projects above the general level. 



Case No. II (Fig. 2). It is unfortunate that this specimen is no 

 more than a fragment; l)ut, fragmentary though it is, one cannot 

 afford to neglect it. It consists of the right half of a horse's mandible 

 broken off anterior to the first cheek-tooth. The first tooth (pm^) has 

 been lost; but, judging from its alveolus, it was evidently perfectly 

 natural in form and size. The teeth from pm^ to m^ inclusive, do 

 not offer any points of interest: they are normal in every respect, 

 m^ only differs from the normal in having its narrow posterior end 

 curved over to the outside because of the crowding produced by the 

 presence of the supernumerary tooth. This displacement is not nearly 

 so great as in specimen No. I. 



The extra molar (m^) is very well developed and projects con- 



