COMPARATIVE ANATOMY. 131 



ideavour, shall we get rid of the lips, the gums, the teeth ; 

 and acquire, in the place of them, pincers of horn ? By 

 what habit shall we so completely change, not only the 

 shape of the part, but the substance of which it is compos- 

 ed 1 The truth is, if we had seen no other than the mouths 

 of quadrupeds, we should have thought no other could have 

 been formed ; little could we have supposed, that all the 

 purposes of a mouth, furnished with lips, and armed with 

 teeth, could be answered by an instrument which had none 

 of these; could be supplied, and that with many additional 

 advantages, by the hardness, and sharpness, and figure, of 

 the bills of birds. 



Every thing about the animal ?nouth is mechanical. The 

 teeth of fish, have their points turned backwards, like the 

 teeth of a wool or cotton-card. The teeth of lobsters, work 

 one against another, like the sides of a pair of shears. In 

 many insects, the mouth is converted into a pump or sucker, 

 fitted at the end sometimes with a wimble, sometimes with 

 a forceps; by which double provision, viz. of the tube and 

 the penetrating form of the point, the insect first bores 

 through the integuments of its prey, and then extracts the 

 juices. And, what is most extraordinary of all, one sort of 

 mouth, as the occasion requires, shall be changed into an- 

 other sort. The caterpillar could not live without teeth ; 

 in several species, the butterfly formed from it, could not 

 use them. The old teeth, therefore, are cast off with the 

 exuvire of the grub ; a new and totally diiferent apparatus as- 

 sumes their place in the fly. Amidst these novelties of form, 

 we sometimes forget that it is, all the while, the animal's 

 month-, that whether it be lips, or teeth, or bill, or break, 

 or shears, or pump, it is the same part diversified ; and it 

 is also remarkable, that under all the varieties of configura 

 tion with which we are acquainted, and which are very 

 great, the organs of taste and smelling are situated near 

 each other. 



in. To the mouth adjoins the gullet; in this part also, 

 comparative anatomy discovers a diflference of structure 

 adapted to the different necessities of the animal. In 

 brutes, because the posture of their neck conduces little 

 to the passage of the aliment, the fibres of the gullet, which 

 act in this business, run in two close spiral lines, crossing 

 each other ; in men, these fibres run only a little obliquely 

 from the upper end of the CESophagrus to the stomach, into 

 which, by a gentle contraction, they easily transmit the 

 descending morsels that is to say, for the more laborious 



