STOMACH 917 
venting substances such as grass, 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 cuticular 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 
Casuarius, Dromexus, Sphenisci, Podicipedidx, Steganopodes, Herodiones, 
Pheenicopterus and Ciconix ; and, though less apparent, by Lhea, 
Mergus and the fallidx. Since most of the birds thus furnished 
are piscivorous, it seems more reasonable to connect this arrange- 
ment with 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 Phalacrocoraz, 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 Dromzxus, and in certain 
Tanagers, Huphones, 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 
Corvide 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 
lamellz, 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 
