Mr Nasmyth on the Human Mouth. 173 



in all sorts of ways ; and thus his mouth has a prehensile cha- 

 racter. He also uses his teeth as instruments for punishing 

 his enemies, seizing his prey, and separating the assimilative 

 portions of his food from those which are not. In fact, 

 they assist him on all occasions, and the forcible tearing which 

 is habitually exacted from him, owing to his want of artificial 

 instruments, and the little assistance he derives from cooking, 

 tend, most decidedly, to evert both the upper and the under 

 jaw. Even at the earliest period of uncivilized existence, 

 habits prevail which powerfully contribute to that extra de- 

 velopment which produces the prominent mouth. We learn 

 from actual observers, that the uncivilized mother suckles her 

 offspring for the protracted period of two years or more, and 

 that the prominent mouth does not exist in infancy ; but its 

 development is assisted by the habit of long sucking, which 

 acts powerfully on the then very plastic condition of the bones 

 of the jaw. Indeed, in social life, we have frequent examples 

 of the modified effect of habits giving a like tendency in in- 

 fancy to the protrusion of the anterior portion of the upper 

 j^aw, such as the child being allowed to suck its tongue or its 

 fingers, or having to be fed for a long period from a hard 

 bottle. 



Acts calculated to have an effect in moulding the jaw are 

 not limited to infancy ; they may extend throughout life ; and 

 the prominent development will always be found in proportion 

 to the ratio of power of the under jaw ; and we have not only 

 seen how well the anatomical arrangement of the osseous 

 parts admit of these mouldings, but we must be satisfied that 

 the design is perfect in allowing of such modifications ; other- 

 wise they would have been constantly exposed to injury by 

 force from without, and concussion from within. This plas- 

 ticity, however, is limited. An examinatioti of the skeletons 

 of individuals with prominent jaws will demonstrate that it is 

 a simple modelling of the original quantity of material which 

 is affected. Beyond a full and perfect development of the 

 parts, there is no peculiarity excepting the eversion of the ma- 

 terial, or the placing of it in an altered position. 



To form the mouth of any other animal than man, difference 

 of structure, and a different specific quantity of material, be- 



