VOL, XXI.] rHILOSOPHICAL TKANSACTI0N3. 403 



readily penetrate a substance that is hard, and which the incisores can scarcely 

 make any impression on. And as the parts of a more solid body are commonly 

 with more difficulty separated, and there must be a greater stress put upon those 

 teeth which pull it into pieces; so these teeth are much more firmly fixed in 

 the jaws than the incisores, though they have but one single root. Besides, 

 the position of all these teeth is accommodated to their use, as being planted 

 opposite to the aperture of the mouth, so that they may be conveniently ap- 

 plied to the substance we have to eat, before it is broken, and when it is too 

 large to be admitted within the mouth. 



The teeth which by a compression and attrition reduce the little morsels 

 to smaller parts are, from the manner in which they break the aliment, called 

 denies molares, because they grind the food like so many little mill-stones. 

 And that they might be rendered fit for this purpose, they are made broad at 

 that extremity which stands out of the gums, by which means they retain some 

 quantity of the food between them every time the lower jaw is pulled up and 

 forced against maxilla superior. And as they are broad, so they are formed with 

 inequalities and protuberances, and by the motion of the lower jaw from one 

 side towards the other they grind what lies between them into pieces. The 

 position of these teeth too is as convenient as that of the incisores and the 

 dentes canini: for being designed to break those pieces of our solid food, which 

 are taken into the mouth, and these pieces, when they are compressed and 

 moved by the dentes molares, being apt to fiy out of the mouth if there were 

 no contrivance to prevent it, they are placed beyond the aperture of the mouth, 

 and opposite to the cheeks, which keep the food within that cavity ; and not 

 only so, but press it in between the dentes molares on one side, as the tongue 

 does on the other, until they have sufficiently broken and divided it. 



At the same time, whilst the dentes molares are breaking the food, there 

 flows into the mouth a salival juice, which mixes with it, and not only serves 

 to moisten it and to render it more apt and easy to be divided, but seems to be 

 the ferment, by the benefit of which the food is dissolved and digested ; and 

 therefore it is intimately mixed with it by the teeth agitating them together in 

 mastication. 



This liquor, which we commonly call the saliva, or spittle, seems to be a 

 composition of two several juices, very different in their natures; and there- 

 fore the several parts of it are separated by their proper glands, and nature lias 

 planted no fewer than four pair about the mouth, which supply the juices that 

 make the saliva, viz. the parotides, and the glandulae nuckianas, the glandulaa 

 maxillares internae, and sublinguales. Not that I suppose, as there are four 

 pair of salivary glands, so there are four sorts of juices supplied from them, 



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