314 GENERAL ORNITHOLOGY part ii 



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 ex- 

 treme case of emesis offered by birds is witnessed in the hornbills 

 {BitMrotidce) which have been known to throw up the coat of their 

 stomach without discomfort, — 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 American 

 vultures (Cathartides). Fish-eating birds, as herons, gulls, petrels, 

 habitually vomit when wounded or otherwise molested. 



The Proventrieulus. — 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 proventrieulus; whatever its size or shape, or 

 whatever its magnitude in comparison with the grist-mill, it is re- 

 cognised by the presence in its mucous surface 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 recognised 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 (Pig. 101, ^,j). 



The Gizzard. — Mixed with the salivary, ingluvial, proventri- 

 cular and other secretions of the mucous surface, and already 

 chymified, the food of birds next passes directly into the gizzard, 

 gigerium, or muscular division of the stomach, sometimes called the 

 ventriculus bulbosus. The two are ' sometimes separated by a tract, 

 sometimes immediately consequent. In the muscular gizzard, the 

 food-grist is ground fine. To this end, the walls of the cavity be- 

 come developed into a more or less powerful muscular apparatus, 

 and the mucous membrane changes to a tough, thick, horny, occa- 

 sionally even bony, lining ; this callous cuticular lining being often 



