STOMACH 917 



venting substances sucli as gi'ass, fragments of bone, or sharp 

 stones from entering the small intestine, while smooth seeds, 

 however hard, pass freely. 



What may be deemed a third compartment of the Stomach is 

 possessed by many birds. This is the so-called pyloric bulb, 

 belonging to the Gizzard and not to the Duodenum, since it 

 contains the same cuticulai- lining as the former ; and, although as 

 regards the latter cut off by a constriction, ending towards it by 

 the typical pyloric sphincter. This arrangement is possessed by 

 Casiiarius, Dromseus, Sphenisci, Podicipedidas, Steganopodes, Herodiones, 

 Fhcenicopterus and Ciconise ; and, though less apparent, by Rhea, 

 Mergus and the Ballidm. Since most of the birds thus furnished 

 are piscivorous, it seems more reasonable to connect this arrange- 

 ment -^vith their very watery food than to regard it as a Reptilian, 

 notably Crocodilian, feature. 



Two kinds of Gizzard, the Simple and the Compound, may be 

 conveniently distinguished, though they are connected by inter- 

 mediate stages, and thus only the extreme forms are fit for general- 

 ized description. 



1. The Simple Gizzard may be oval, globular or sack-shaped, 

 each of the slightly-flattened sides containing a weak operculum, 

 while the "walls are always thin, capable of considerable distention, 

 and mostly of a pale bluish-yellow, rarely reddish, colour. The 

 tunica mucosa contains numerous simple glands, secreting a soft 

 cuticular lining which is continuously renewed and easily peels 

 off as a viscous yellow coating. Such a Gizzard is possessed 

 by the birds that feed chiefly on fish, flesh, soft fruits and insects. 

 In many piscivorous birds, such as Ardea and Phalacrocorax, it is 

 transformed into a long oval sack occupying the greater part of the 

 ventral and left space of the abdominal cavity, and reaching to the 

 cloacal region. In other piscivorous birds, however, Phaethon, 

 Pelecanus and Sula, as well as in Casuarius and Dromseus, and in certain 

 Tanagers, Euphones, the Gizzard is much reduced in size, while its 

 functions are assumed by the much enlarged Proventriculus. The 

 relation between the strength of the Stomach and the nature of the 

 food is clearly shewn by Manucodia, which feeds on soft fruit and 

 has very thin walls to its Gizzard, whereas in the omnivorous 

 Cm'vidx they are very muscular. 



2. The Compound Gizzard possesses conspicuous tendinous 

 opercula, a pair of intermediate and a pair of strong lateral muscles. 

 The interior is lined with a thick brownish cuticle, formed by the 

 hardened secretion of the tunica mucosa, and consisting of numerous 

 lamellae, which are continuously reproduced by the secreting cells to 

 supply those that are worn down by constant trituration of the 

 food through the action of the lateral muscles. The cuticular 

 covering of the middle muscular or part of each of these muscles 



