[ 3 1 1 ] 
form, which ferve as fo many grindflones for re- 
ducing their food to a powder, before it be con- 
veyed into the ftomach for digeftion ; and when fo 
prepared, it is, with regard to the digeftive power, 
become fimilar to animal food : therefore in many 
fuch animals the ftomach is fimilar to that of the 
carnivorous ; and whenever the ftomach in gra- 
nivorous quadrupeds differs from this general rule, 
there is a Angularity in the operations of digeftion. 
Such birds as live upon this kind of food, for the 
digeftion of which trituration is indifpenfably 
neceffary, have the powers of maftication and di- 
geftion united in one part ; which is of a pecu-. 
liar ftrudture for that purpofe ; this is the gizzard. 
In granivorous birds therefore one fingie organ an- 
fwers both to the teeth and ftomach of granivorous 
quadrupeds, and confequently the gizzard alone of 
birds will point out the food of the fpecies as 
clearly, as the teeth and ftomach together do in 
other animals, in which the two offices of mafti- 
cation and digeftion are not joined together in ffie 
fame part. 
As it appears then to be the difference of the 
ftomachs only, that fits birds for their different 
kinds of food, it is evident that every gradation of 
ftomach mu ft be found among them, from the true 
gizzard which is one extreme, to the more mem- 
branous ftomach which is the other; fince the food 
of different fpecies is of every different kind, from 
the hardeft grain, to the fofteft animal matter. In 
confequence of this, it muft be as difficult to deter- 
mine the exadt limits of the two different conff ruc- 
tions, to which the names of gizzard and jlomach 
ipeci- 
