148 The Cardiac Glands of Mammals 
tia, composed of animals that are as distinctly herbivorous as the Myo- 
morpha, no such specialization has taken place. On the other hand, the 
fact that in the purely herbivorous Kangaroos, in the leaf-eating sloths, 
and in the graminivorous and herbivorous Rodents and Ungulates, simi- 
lar differentiations of the stomach have arisen independently, is surely 
worthy of serious consideration. Another factor which is discussed by 
Fleischmann is a possible correlation between dental evolution and gas- 
tric structure. He found, however, that in various species of Arvicola 
there was no relation between the complexity of the molar pattern 
and the structure of the stomach. In any case in the writer’s opinion 
the principle of correlation would not explain, except in a general way, 
the increasing complexity of the stomach. The direct effect must be 
exerted through the food. The occurrence of similar specializations in 
certain Anteaters and in the Cetacea, which subsist on food which is in 
a sense the chemical antithesis of that of the herbivors renders it neces- 
sary to seek the causes of this specialization in conditions which are 
common to all the animals which possess it. If we conclude that the 
object of the complex structure of the ruminant stomach is simply to 
provide increased storage capacity or an antechamber to the stomach in 
which carbohydrate digestion can go on, then we must seek for wholly 
different causes in the Cetacea and Anteaters. It seems more probable 
that similar causes have operated in all the various instances and that 
chemical composition has been important only imasmuch as it deter- 
mined the bulk and consistence of the food masses in the stomach. Any 
discussion of the methods by which these changes have been effected 
must for the present be largely speculative, and the final solution of 
the question must rest with the experimental physiologist. There are, 
however, a number of facts which indicate that the causes have been of 
a physical, mainly mechanical, nature. 
I have already pointed out that in all these stomachs it is probable 
that the change began at the cardiac orifice and proceeded gradually 
into the stomach, encroaching more and more upon the normal glandu- 
lar mucous membrane. This is exactly paralleled aceording to the ex- 
perimental researches of Ellenberger, 90, by the course of the food. 
According to this investigator, the food does not “ circulate” in the 
stomach of the horse, but accumulates as it is swallowed in the left ex- 
tremity of the stomach in the fundus sac. When food is again taken 
that previously swallowed is displaced en masse in the direction of the 
pylorus by the new food which is in turn similarly displaced by the next 
meal. ‘There is thus a gradual progression of the food from cardia to 
pylorus. During this process the food is undergoing various changes. 
