172 Mr Nasmyth on the Human Mouth. 



ment are some of the penalties of the irrational habits of 

 social existence, and are never to be found amongst uncivi- 

 lized races. Amongst races existing in a good climate, and 

 where there is no deficiency of exercise or nourishment, a 

 perfect development of the mouth, as well as of all other 

 parts, follows. There is then a regular symmetrical arrange- 

 ment of the teeth, the best adapted for perfect articulation, 

 and for mastication, leaving the teeth perfectly arranged, 

 and fully developed. The entire range then forms a per- 

 fect parabola, each tooth standing nearly perpendicularly to 

 the portion of the alveolar ridge to which it is attached ; 

 and that, it is evident to me, is their normal development. 

 That disposition is to be found in the vertical moiith of the 

 Caucasian races, which, in my opinion, must have been the 

 original development of mankind ; and from which there is 

 no difficulty in tracing all the varieties of the human species 

 which have ever appeared on the face of the earth. 



Having attempted to explain the deviations from this typo 

 in the dental organs of social life by neglect of the exercise of 

 the functions of the parts, I shall next endeavour to shew how 

 abuse, in a contrary line of habit, produces a development 

 in an exactly opposite direction. I have described the arrange- 

 ments which afford an extensive latitude of plasticity in the 

 upper jaw, admitting of the parts to be modelled by the exer- 

 cise of their ordinary functions. But in uncivilized life, ex- 

 traordinary functions are called into action, and a great excess 

 of energy is also thrown into those of an ordinary descrip- 

 tion. 



The ordinary duties required of the mouth in bivilized life, 

 as I have observed, are a moderate exercise of power for di- 

 vision, tearing, and comminution, or grinding. In uncivilized 

 life, however, there are superinduced upon these more powerful 

 exactions, which have a great controlling influence over thd 

 development of the parts. Man, in the uncivilized state, has 

 but few instruments or tools to assist him in operations of any 

 kind, and his teeth are ready substitutes, which, on all occa- 

 sions,, from infancy to old age, he most unscrupulously resort;^ 

 to. He attacks the roughest materials of all kinds with his 

 teeth. He uses them to form and to fashion those materials 



