212 
GENERAL OMNITHOLOGY. 
gullet of many small birds, as various genera of Fringillidce and Corvidce, is much more disten- 
sible than is commonly supposed, and may be found crammed with seeds which there find rest- 
ing-place for some time. The fish-eating birds, as herons, cormorants, loons, and others, have 
also capacious gullets. The Australian bustard, Eupodotis australis, has an oesophagus capa- 
ble of such extraordinary distension that it hangs down in front of the breast when inflated 
with air, as it is in the amatory display in which that species is wont to indulge. Aside from 
mere distensibility of transient character, the oesophagus of many birds becomes modified 
anatomically into a special pouch, — the crop or craw, ingluvies, where the food is detained to 
be macerated in a special secretion before passing on to the true stomach. Such definite crops 
occur in birds of prey, which gorge such masses of food in their irregular voracious banquets 
that it cannot all be received into the stomach at once j and likewise throughout the orders of 
Columbine and Gallinaceous birds, which habitually feed upon seeds and other fruits so hard 
that they are advantageously macerated as a preliminary to true digestion. The common fowl 
furnishes a good illustration of a large, definite, single and median crop ; in pigeons it is a pair 
of lateral dilatations (see frontisp.). In these latter birds, when they are rearing their young, 
the secretion of the ingluvies,, always copious, becomes still more so, and of a milky character in 
consequence of the activity of the altered mucous surface ; it is regurgitated into the mouths of 
the young, along with the macerated grains. This phenomenon is the nearest approach in 
the class of Birds to the characteristic mammary function of a higher class ; and the analogy 
of the 'pigeon's milk' to the lacteal secretion of the Mammalia lias not escaped popular notice." 
Various other birds also feed their young by regurgitation of elaborated food ; and very many 
similarly reject indigestible portions of their ingesta. Such vomiting is best known tc» be the 
wont of birds of prey, which habitually throw up the hair, feathers and bones of their victims, 
made up into the boluses called " castings"; but the practice is far from being confined to these 
flesh-eaters. The extreme case of emesis ofi'ered by birds is witnessed in the horn-bills 
(BucerotidcB) which have been known to throw up the coat of their stomach without discom- 
fort, — what a blessing it would be to some old topers if they could do the same, and grow 
another with equal ease ! In fact, in consequence of the capacity and directness of the gullet, 
vomiting is very easy to birds, and with some it is a means of self-defence, — very effectual 
for instance in the cases of our vultures {Cathartides). Fish-eating birds, as herons, gulls, 
petrels, habitually vomit when M'^ounded or otherwise molested. 
The Proventriculus. — The tube just considered ends below in a special tract, variously 
dilated or not, but always peculiar in the presence of certain gastric follicles which secrete the 
digestive fluid proper. The stomach " of a bird, in fact, is compound, consisting of a glandular 
or digestive portion, and a muscular or grinding part. The former is the proventriculus; 
whatever its size or shape, or whatever its magnitude in comparison with the grist-mill, it is 
recognized by the presence in its mucous surfiice of these gastric follicles, secreting the peptic 
fluid which chymifies the food. The follicles are perhaps always large enough for this part of 
the tube to be recognized by the naked eye, — the mucous membrane having here a thickened, 
velvety, vascular appearance. The glands are of various sizes and shapes, — usually simply 
tubular, sometimes clubbed or conical, or variously racemose (like a bunch of grapes). They 
are disposed in a zone around the tube, or in patches upon part of its surface, — in the darter 
(Plotus) , very singularly in a separate lateral compartment looking like a crop. Details of the 
grouping of these solvent glands are interminable. Whatever its anatomical variations, and 
however like the end of the oesophagus it may simply appear to be, this ventriculus glandulosus 
is the bird's proper stomach (fig. 101, j). 
The Gizzard. — Mixed with the salivary, ingluvial, proventricular and other secretions of 
the mucous surface, and already chymified, the food of birds next passes directly into the giz- 
