iVlr Nasmyth on the Human Mouth. 16? 



serted into the coronoid processes, and situated between the 

 fulcrum residing in the condyles, and the weight to be over- 

 come produced by the substances for comminution placed 

 between the teeth in any situation around the dental arch, 

 but always anterior to the power exerted by the temporal 

 muscles. Other muscles (the masseter and pterygoid) in- 

 serted into the under jaw, and deriving their origin from 

 points of the bones forming the superior portion of the face, 

 may be looked upon more in the light of controlling powers 

 than otherwise. At the same time, they afford a direct cer- 

 tain assistance in elevating the under jaw, but their cha- 

 racteristic sphere of action is in varying and regulating the 

 chief power produced by the temporal muscles. The princi- 

 pal duty of the remaining large muscle of the under jaw, the 

 buccinator, is that of perfecting the parietes of the mouth. 

 It forms an antagonist to the tongue in receiving the food 

 into the mouth for mastication, and in retaining it within 

 the influence of the grinding apparatus. This beautiful 

 piece of machinery, taken as a whole, may be considered in 

 the light of an inverted hammer and anvil, the hammer per- 

 forming its work on the anvil of the superior jaw ; and the 

 machinery is perfect. 



But these, aided by the muscles connected with the chin, 

 the tongue, the lips, and the fauces, have another duty of 

 great delicacy and extent to perform, namely, that of articu- 

 lation. This very essential function is the result of the com- 

 bined action of all these muscles, through peculiarly delicate 

 modifications, produced on the air that has been undulated 

 into a sonorous state in its passage through the rima glot- 

 tidis. In addition to this general view of the machinery and 

 uses of the mouth in man, it will be necessary to examine a 

 little more minutely the constituents of the skeleton of the 

 mouth, and learn how that enduring portion in which the 

 shape or ethnographic signs reside and become permanent 

 is affected, in different tribes, by the exercise of the functions 

 exacted from the various parts. In this point of view, it may 

 be useful to consider the mouth under three divisions : an 

 anterior, posterior, and median. We shall, in that way, be 



