g16 STOMACH 
STOMACH. This important organ in the DIGESTIVE SYSTEM 
(p. 136) consists of an anterior portion, the Proventriculus, which is 
glandular, and a posterior, the Ventriculus or Gizzard, which is 
muscular—the former being characterized by specific glands, and in 
size standing in inverse proportion to the latter. In many Birds, 
however, especially those which feed upon Tishes, both portions are 
wide and pass gradually into one another; but in the majority the 
Proventriculus is much the smaller, and is separated from the 
Gizzard by a marked constriction, devoid of glands. The 
glands themselves vary greatly in size and position, being 
however generally packed close together in a broad ring ; but, when 
the Proventriculus is wide, as in Casuarius, Aptenodytes and the 
Tubinares, either scattered with wide interstices, or collected in 
patches leaving the greater part of the walls free. In Leptoptilus 
argala, in Phalacrocoraz and in Plotus levaillanti two such patches 
exist, while in P. anhinga they are gathered into one globular mass, 
as big as a hazel-nut, attached to the outside of the Stomach, and 
opening into the right dorsal wall of the Proventriculus. Shea 
possesses a round dorsal patch, and one similar occurs in the 
embryo of Sfruthio, but is subsequently drawn out into a dumb-bell 
shaped area, which, owing to the peculiar distortion of the whole 
Stomach, eventually occupies the greater part of the dorsal wall. 
In most carnivorous and piscivorous Birds, in the Laro-Limicole, 
Columbx and Passeres, the individual glands are small and simple; 
but larger and more complicated in most herbivorous and grani- 
vorous Birds, especially the Ratitz and Gallinz. 
The Gizzard occupies most of the middle and left part of the 
abdominal cavity, its Cardia or upper end looking toward the 
vertebral column, and slightly inclined to the left side, while the 
Pylorus or lower end is turned toward the right. The surrounding 
muscular fibres are disposed in more or less. regular spirals, possess- 
ing in their course two tendinous intersections, producing as many 
tendinous opercula, one on each side ; and though, taken as a whole, 
they form only one muscle, the entire mass is generally spoken of 
as consisting of a right and a left muscle. The Gizzard varies 
greatly in size, shape, strength and position—chiefly according to 
the kind of food. When the organ is very muscular, as in 
Pigeons, Fowls and Ducks, it takes the form of a biconvex lens, 
with a sharp dorsal and ventral margin. On the whole the walls 
retain the same layers as those of the rest of the alimentary canal (p. 
137); but the muscular layer is more strongly developed, while the 
tunica mucosa contains mucous glands alone, and none producing any 
specific or chemically-acting secretion. The function of the Gizzard, 
beyond serving as a receptacle of food, is therefore purely mechanical. 
The Pylorus (cf. p. 138, fig.) is almost always guarded by a 
special muscular sphincter and several inner valve-like ridges, pre- 
