DIGESTIVE ORGANS. 225 
The shape of the stomach is to some extent dependent upon the 
shape of the body. In the elongate species it lies in the axis of the 
trunk, especially in the lower vertebrates (fig. 227, a), but with increase 
in the body width it becomes more transverse. This involves a bending 
and a torsion of the tube, always to the right, and results in two faces 
or ‘curvatures,’ a lesser or anterior, and a greater or posterior, the 
greater curvature often expanding into a so-called fundus region. 
The end of the stomach which connects with the cesophagus is nearest 
the heart and hence is called the cardiac end. 
In the fishes the stomach may be either straight or saccular, often assuming the 
form of a blind sac (fig. 227, g). The line between cesophagus and stomach is not 
well marked, as the cesophageal folds may continue into the stomach. The teleosts 
exhibit the greatest variety in shape, in correlation to the differences in food. All 
gastric glands are lacking in the cyprinoids, while Amia has both cardiac and pyloric 
glands, and, like many teleosts, the stomach is ciliated. In the amphibians and 
reptiles the distinctions between cesophagus and stomach are more marked, most 
in the crocodiles. In the amphibians the ciliation of the mouth is continued into 
the stomach. 
In the birds there is a differentiation of the gastric region into two 
regions, an anterior glandular stomach or proventriculus, and a pos- 
terior muscular gizzard. The proventricular glands secrete a diges- 
tive fluid, and the food, mixed with this, is passed on to the gizzard. 
The walls of the latter have their muscles developed into a pair of discs 
with tendinous centres, while the glands of the gizzard form a secretion 
which hardens into a horny (keratoid) lining, sometimes developing 
into tubercular structures, of great use in grinding the food, thus in part 
making good the absence of teeth. In the grain-eating birds small 
pebbles are taken into the gizzard and are used in triturating the food. 
(In the fossil pterodactyls small clusters of stones are sometimes found 
in such a position as to lead to the supposition that these reptiles also 
had'a gizzard.) The gizzard is best developed in the grain-eating 
birds and is weakest in the birds of prey. In one species of pigeon 
part of the wall of the gizzard is ossified. 
The mammalian stomach shows the greatest range of form (figs. 
227, 228) and the greatest development of different kind of glands. 
It may be a simple sac or it may be subdivided into a series of chambers. 
It may be almost wholly cesophageal in character (Ornithorhynchus, 
fig. 228, A). Occasionally the cardiac glands may be absent. It 
may be a simple sac, longitudinal or transverse in position, or it may be 
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