Mr. Home on the Gizzards of Grazing Birds. 185 
with digestion, in these animals who naturally live wholly on 
grass, I was led to consider that as some birds graze, there 
must in them be peculiarities in the form of their gizzards, to 
lit them for digesting this particular kind of food, by which they 
may readily be distinguished from the gizzards of other birds. 
With this view, I examined the gizzards of the goose and 
swan, who are both in the habit of grazing, (though geese 
more constantly so,) and compared their structure with that 
of the turkey, a bird nearly of the same size, whose food is of 
a different kind. 
To make this comparison more correct and satisfactory, a 
goose's and a turkey’s gizzard were moderately filled with 
plaister of Paris, and then boiled ; by this means the cavity 
was kept open, and the course of the muscular fibres very 
readily traced. 
In the turkey, the external surface was first attentively 
examined, viewing that side which is anterior in the living 
bird, and on which the two muscles and middle tendon are 
most distinct, there being no other part to obstruct the 
view ; while on the opposite side there is the opening of the 
pylorus, and the bag formed by the lower portion of the 
gizzard beyond the circumference of the muscles. 
In this view', the muscle on the left side distinctly larger 
than that on the right, as will be seen in the annexed draw- 
ing. This appears on reflection to be a great advantage in pro- 
ducing the necessary motion ; for if the two muscles were of 
equal strength, they must keep up a greater degree of exer- 
tion than is necessary ; while in the present case, the principal 
effect is produced by the left side, and a smaller force is used 
by the right, to bring the parts back again. 
