212 GENERAL OBNITHOLOGY. 



ffullet of inauy small birds, as various genera oi FringillidfB and Corvida;, 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 infiated 

 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 ojsophagus 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 ; 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 has 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 to 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 off'ered by birds is witnessed in the horn-bills 

 (BueerotidcB) 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 wounded 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 surface of these gastric follicles, secreting the peptic 

 fluidwhich cMjmifies 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 havhig 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 a?sophagus it may simply appear to be, this ventricidus glandulosus 

 is the bird's proper stomach (fig. 101, i, j). 



The Gizzard. — Mixed with the salivary, ingluvial, proventrieular and other secretions of 

 the mucous surface, and already chymifled, the food of birds next passes directly into the giz- 



