Mr Nasmyth on the Human Mouth. 1&9 



ill object. The anterior portion possesses the central inci- 

 sors, but the power of their full exercise is not adapted to 

 transfix, divide, and tear, in a manner similar to that exer- 

 cised by the powerful tooth we have just alluded to. They 

 are the most distant from the power which acts on the jaw ; 

 and in the upper jaw they present a broad and chisel- shaped 

 cusp, instead of the pointed and piercing cusp of the canine 

 tooth, and the root even of the upper central incisor is 

 about one-third less than that of the canine. On the whole, 

 then, they have only about one-third of the power which the 

 canine teeth have; and they are consequently only applicable 

 to the division of small objects, which, as their name implies, 

 is their true duty, assisted by the lateral incisors. The pos- 

 terior division contains the machinery peculiarly adapted to 

 the process of grinding or comminution. There is a central 

 sphere of activity here likewise. That resides in the first 

 large grinder, which is the standard tooth of division or com- 

 minution, crushing every thing with great force upon which 

 it is brought to act. In this duty it is materially and most 

 efficiently assisted by the two small grinders in front, and 

 the second and third large grinder behind. The centre of 

 its action nearly corresponds with the centre of the great 

 moving power of the jaw ; so that there is a great concentra- 

 tion of force in this division. Such, then, are, generally, the 

 duties exacted from these parts throughout all the races of 

 mankind ; and having already explained the machinery by 

 which the fulfilment of these duties is provided for, I come 

 now to point out some peculiar considerations connected with 

 the skeleton of the mouth, which will assist in explaining the 

 ethnological signs exhibited in the parts. 



The most recognizable etiinological features are to be found 

 in the anterior division, which presents, on the one hand, the 

 prominent jaw and everted teeth of the Negro, more parti- 

 cularly ; and, on the other side, the crowded and irregularly- 

 arranged teeth and perpendicular jaws of the Caucasian tribes. 

 Both the other divisions of the dental arches, however, dis- 

 play, in like manner, characteristic features corresponding with 

 these two states of existence, and which I shall endeavour suc- 

 cessively to bring under attention. The anterior portions' of 



