9i6 STOMACH 



STOMACH. This important organ in the Digestive Systeji 

 (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 Fishes, 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 

 Grizzard 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 

 Tuhinares, either scattered with wide interstices, or collected in 

 patches leaving the greater part of the walls free. In Leptoptilus 

 argala, in Fhalacrocorax 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. Ehea 

 possesses a round dorsal patch, and one similar occurs in the 

 embryo of Struthio, 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-Limicolse, 

 Columbas and Passeres, the individual glands are small and simple ; 

 but larger and more complicated in most herbivorous and grani- 

 vorous Birds, especially the Ratitx, and Gallinx. 



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 land 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- 



