•320 HISTORY OF 



merit will suffice to convince 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, the lower 

 falls, and the table remains untouched between them. The 

 upper jaw has motion as well as the under; and, what is remark- 

 able, 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 painters call under- 

 hung; and they consider this as a great defect in beauty.' 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 pas- 

 sion, 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 motion is ; and that for one person to yawn, is suffi- 

 cient 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 jaw dislocated ; so that when he opened his 

 mouth wdder 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 sympathe- 

 tic 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. "- 



In all animals. However, the parrot is an obvious exception ; and so is inMi 

 hil^self^ as shown above. 



I Mr Buffon says, that both jaws, in a perfect face, should be on a level ; 

 but this is denied by the best painters. 



'i. Since the publication of this work, the editor has been credibly iu. 

 formed, that the professor had not the defect here mentioned. 



