MAMMALIA. 5 



wliicli it is lined in the interior. The fourth cavity, which is the 

 true stomach, has received the name of caiUdte, or rennet-bag, 

 because it has the proj)erty (on account of the gastric juice with 

 which its surface is saturated) of causing milk to coagulate. 

 The first three stomachs, the j)fiunch, the honey-comb bag, 

 and the many-plies, commimicate with the ccsophagus, so as to 

 allow the aliment to return easily into the mouth. 



From the rennet-bag, the food, going through an opening 

 called the pylorus, passes into the intestines. There the alimentary 

 mass yields all its nutritious elements, and is then evacuated. 



The length of the intestines varies in the Mammalia according 

 to the kind of food they eat. Thus, in the Carnivora, their length 

 is only three or four times as much as the length of the animal's 

 body ; while in the Herbivora the intestines are from twelve to 

 twenty-eight times its length. In the domestic Cat the intestines 

 are proportionately longer than in any of its wild congeners, 

 having thus gradually become adapted (in a long series of genera- 

 tions) to a less exclusively carnivorous regimen. 



The apparatus for the circulation of the blood has for its central 

 organ the heart — a hollow muscle, composed of four cavities : two 

 auricles and two ventricles. In all Mammalia there is a double 

 circulation of the blood ; there exists a great and a little circula- 

 tion. ' The venous blood which comes from all parts of the body 

 into the right auricle of the heart, conveyed by the hollow veins, 

 passes first into the right ventricle, which sends it through the 

 pulmonary artery to the limgs. There it is transformed into 

 arterial blood — that is to say, it absorbs the oxygen of the air ; 

 then it returns to the left auricle by the pulmonary veins. Thence 

 it passes into the left ventricle of the heart, and discharges itself 

 into the artery called the aorta, and thence into the other arteries, 

 which distribute it throughout the whole body. The blood then 

 comes back from all parts of the animal's body into the right 

 auricle of the heart by the veins — consequent upon the conr- 

 mrmication which is established between the veins and arteries, 

 in the immediate vicinity of the tissues, by the general capillary 

 net- work or sj^stem. 



The respiratory apparatus occupies, in Mammalia, the upper 

 part of the bony framework formed by the ribs and the sternum, 

 or breast bone. This apparatus is composed of lungs — double 



