Dif/estive Organs of Birds. 129 
to the agreement of their digestive apparatus, but that the groups 
thus produced would be perfectly natural, in respect at least to 
their principal habits. 
It is not of much importance with what tribe of birds we begin ; 
but as the rapacious species generally take the lead in systems, I 
shall not deprive them of their rank. And here, once for all, I must 
remark, that in every particular, the descriptions will be entirely 
original, that is, the result of my own observation. 
I. Digestive Organs of the Diurnal Rapacious Birds. 
As unexceptionable representatives of the aquiline and buteonine 
groups of this order of birds, we may take the Golden Eagle, Aquila 
chrysaetus, and the Common Buzzard, Buteo vuigaris. 
Plate IV. represents :-Fig. 1. the bill, 2. the palate, 3. the tongue, 
4. the intestinal canal, 5. the rectum and caeca, of the Golden Eagle, 
one-third of the natural size ; Fig. 6. a section of the proventriculus, 
7- some of its glands, 8. the pylorus : -6 and 8. of the natural size, 
7, enlarged. 
The bill of the Golden Eagle, Plate IV. Fig. 1, is shorter than the 
head, very deep, compressed towards the end, with a longish decurv- 
ed tip. The upper mandible has at the base a broad cere, a, or bare 
coloured skin ; its dorsal outline, 6, is slightly convex as far as the 
edge of the cere, then curved so as to form rather more than the 
fourth of a circle ; the ridge, on the cere, is broad and convex, on 
the horny part narrow but convex ; the sides at the base are nearly 
flat and sloping, towards the end erect and slightly convex ; the 
edges towards the base, c, are . soft, being covered with skin, con- 
tinuous with the membrane of the mouth, beyond the nostrils sharp, 
direct, with a slight festoon ; the tip decurved, subrigonal, acute. 
The lower jaw has the crura widely separated at the base, so that 
the angle at the base of the horny mandible is broad and rounded ; 
its dorsal outline, d, is convex, the back broad, towards the end nar- 
rowed ; the sides rounded ; the edges at the base covered with skin, 
towards the end horny, inflected and sharp, and curving downwards 
to the tip, which, viewed vertically, is broadly rounded. The dorsal 
outline of the upper mandible is 2 inches long ; that of the lower 
; the edge of the lower is 2| ; the height of the bill at the nos- 
trils I T V 
The mouth is wide, measuring l-j 7 2 across. The palate, Fig. 2, is 
flat, at the sides smooth and sloping a little upwards, in the middle 
having a longitudinal depression, , into which the tongue fits. This 
depression is bounded by two parallel ridges of skin, having on their 
summit minute papillae directed backwards. In it behind the base 
NO. II. I 
