CHAP, ix.] TEETH ! ORAXG. 201 



able departure from the normal arrangement may be perhaps 

 usefully introduced in illustration of the peculiar variability of 

 the dentition of the group. 



*174. A skull from Borneo in the Oxford University Museum (num- 

 bered 2043 o) has the following extraordinary arrangement. All 

 the teeth are normal and in place except the second premolar of 

 each side in the upper jaw. On both sides there is a large 

 diastema between p l and ^. The diastema on the left side is of 

 about the same size as the normal second premolar, but that on 

 the right side is considerably too small for a normal tooth. The 

 singularity of this specimen lies in the fact that the missing 

 tooth of the right side is present in the skull, but instead of being 

 in its proper place it stands up from the roof of the mouth within 

 the arcade immediately in front of the right canine and almost 

 exactly on the level of the second incisor, being in the premaxilla, 

 at some distance in front of the maxillary suture. 



That this tooth is actually the second premolar which has by 

 some means been shifted into this position there can be no doubt 

 whatever. It has the exact form of the normal second premolar, 

 and is of full size. It stands nearly vertically but is a little 

 inclined towards the outside. The canine is by the growth of 

 this tooth slightly separated from the second incisor, and the first 

 premolar is consequently pushed also somewhat further back. 

 Hence it happens that the diastema for the second premolar on 

 the right side is not of full size. This should be understood, as 

 it might otherwise be imagined that the contraction was due to a 

 complementary increase in the size of the other teeth, of which 

 there is no evidence. 



On the left side of the palate there was a very slight ele- 

 vation at a point homologous and symmetrical with that at 

 which the second premolar of the right side was placed. As it 

 seemed possible that the missing tooth of the left side might 

 be concealed beneath this elevation, a small piece of bone was 

 here cut away, with the result that a tooth of about the same 

 size and formation as Fj was found imbedded in the bone. In 

 this case therefore the second premolar of the right side and of 

 the left side have travelled away from their proper positions and 

 taken up new and symmetrical positions in the palate, anterior 

 to the canines. The facts of this case go to shew that the germ 

 of a tooth contains within itself all the elements necessary to 

 its development into its own true form, provided of course that 

 nutrition is unrestricted. This might no doubt be reasonably 

 expected ; but since the forms of organs and of teeth in particular 

 are by some attributed to the mechanical effects of growth under 

 mutual pressure, it may be well to call special attention to this 

 case, which goes far to disprove such a view. 



175. Specimen having the teeth of the two sides in the lower jaw in 

 extraordinarily asymmetrical disposition. The bone of the jaw does 



