178 ANIMAL PHYSIOLOGY. [LESSON 50. 



tensely vascular ; the left side consists of a hard, callous, insensible, 

 FIG 2g4 non-vascular membrane, comparable in 



every respect to the membrane lining the 

 gizzard of the fowl. An injected prepa- 

 ration of the stomach of the Musk-Rat 

 (so far as it is vascular) is offered in 

 Fig. 284 ; it is useless to attempt to 

 show the other half, for not one single 

 vessel does it possess. But the mucous 

 MUCOUS membrane of stomach, membrane of a true digestive cavity is 

 admirably shown in the vascular portion. 



771. Many of the Rodents (the common Rat, for example) are 

 omnivorous ; feeding indiscriminately upon all that comes in their 

 way ; at one time eating flesh, at another grain. 



772. It has been supposed, therefore, that flesh would be placed 

 in the right side of the stomach, and digested on the principle com- 

 mon to all carnivorous animals ; and that, when a material as re- 

 fractory as wheat was purloined from a farmer's granary, it would be 

 transferred to the left side, and become subject to the same kind of 

 trituration as if found in the gizzard of a fowl. 



773. But inasmuch as all the gnawing animals (Rodents, including 

 even the Mice) possess the same kind of stomach, and many of them 

 are strictly vegetable feeders (Musk-Rat, and others), this opinion must 

 be given up, and at the present moment we can only confess our ig- 

 norance of the intention and special use of this remarkable dual (two) 

 organ. 



774. The wants of those animals designed to feed exclusively on 

 grass, are peculiar, and necessitate an arrangement of the nutrimen- 

 tal organs of such a kind, that no parallel can be found in the animal 

 kingdom, except in certain Insects, organized to consume the same 

 material, and there we find a like adaptation of parts. Of all the 

 various forms of food given to animals as their natural pabulum, none 

 is found to contain such a mere atom of nutrient material as grass. 

 Moreover, the nutriment, small as it is, is locked up in a particular 

 manner, so that the means in ordinary use for the resolution of other 

 substances, are altogether inadequate for the dissolution of a substance 

 so refractory and unyielding. 



775. In the herbivorous quadrupeds (Cows, Sheep, Deer, &c.) we 

 find four distinct sacs, or stomachs, devoted to the reception, macer- 

 ation, and digestion of the food (Fig. 285). 



776. In a state of nature, the herbivora, naturally timid, and 



