194 A HISTORY OF 



" The under jaw in man possesses a great variety of motions ; while 

 the upper has been thought by many to be quite immoveable.* How- 

 ever, that it moves in man, a very easy experiment will suffice to con- 

 vince us. If we keep the head fixed, with any thing between our teeth, 

 the edge of a table, for instance, and then open our mouths, we shall 

 find that both jaws recede from it at the same time ; the upper jaw 

 rises, and the lower falls, and the table remains untouched between 

 them. The upper jaw has motion as well as the under ; and, what is 

 remarkable, it has its proper muscles behind the head for thus raising 

 and depressing it. Whenever, therefore, we eat, both jaws move at 

 the same time, though very unequally ; for the whole head moving 

 with the upper jaw, of which it makes a part, its motions are thus 

 less observable." In the human embryo, the under jaw is very much 

 advanced before the upper. " In the adult, it hangs a good deal more 

 backward ; and those whose upper and under row of teeth are equally 

 prominent, and strike directly against each other, are what the pain- 

 ters call under-hung ; and they consider this as a great defect in beau- 

 ty .t The under jaw in a Chinese face falls greatly more backward 

 than with us ; and, I am told, the difference is half an inch, when the 

 mouth is shut naturally." In instances of the most violent passion, 

 the under jaw has often an involuntary quivering motion ; and often 

 also, a state of languor produces another, which is that of yawning. 

 " Every one knows how very sympathetic this kind of languid mo- 

 tion is : and that for one person to yawn, is sufficient to set all the 

 rest of the company a yawning. A ridiculous instance of this was 

 commonly practised upon the famous M'Laurin, one of the professors 

 at Edinburgh. He was very subject to have his jaws dislocated ; so 

 that when he opened his mouth wider than ordinary, or when he 

 yawned, he could not shut it again. In the midst of his harangues, 

 therefore, if any of his pupils began to be tired of his lecture, he had 

 only to gape or yawn, and the professor instantly caught the sympa- 

 thetic affection ; so that he thus continued to stand speechless, with 

 his mouth wide open, till his servant, from the next room, was called 

 in to set his jaw again."! 



When the mind reflects with regret upon some good unattained or 

 lost, it feels an internal emotion, which acting upon the diaphragm, 

 and that upon the lungs, produces a sigh ; this, when the mind is 

 strongly affected, is repeated ; sorrow succeeds these first emotions ; 

 and tears are often seen to follow : sobbing is the sigh still more in- 

 vigorated ; and lamentation, or crying, proceeds from the continuance 

 of the plaintive tone of the voice, which seems to implore pity. 

 " There is yet a silent agony, in which the mind appears to disdain 

 all external help, and broods over its distresses with gloomy reserve. 



* Mr. Buffon is of this opinion. He says that the upper j&w is immoveable in all ani- 

 indls. However, the parrot is an obvious exception ; and so is man himself, as show n 

 above. 



t Mr. Bufton says, that both jaws, in a perfect face, should be on a level : but this is 

 denied by the best painters. 



* Since the publication of this work, the editor has been credibly irvfonnd th.xt the pre- 

 fessoi had not the defect here mentioned. 



