369 



CLASS IV. 



MAMMALIA. 



We have now reached the class which ranks as the highest of 

 the animal Idngdom ; and to which man himself belongs. 

 Here only do we find organs especially adapted for supplying 

 to the young, during the prolonged period of helpless infancy, 

 that fluid nutriment, to which we give the name of milk. 

 This orgiuiization is so characteristic, that from the Latin 

 word matnmcB, signifying paps or teats, is derived the term 

 mamtruxlia, the scientific appellation by which the class is dis- 

 tinguished. Every animal that suckles its young may, fi'om 

 that circumstance, be referred to the present class. 



Circulation. — The blood is warm, and the heart, as in birds, 

 consists of four compartments. The general arrangement of 

 the arteries through which the aerated blood in man is pro- 

 pelled, is shown in the annexed figure (287) which may be 

 compared with Fig. 241, exhibiting the arterial system in the 

 preceding class. 



" Neither the circulation nor the respiration are quite so 

 active, nor is the animal heat quite so great as in the class of 

 birds."* 



Eespiration. — All the mammalia breathe by lungs. These 

 ai"e not attached to the ribs as in bii'ds, but are suspended in 

 a cavity at the upper portion of the trunk {thorax). They 

 are divided into a multitude of minute cells into which air ia 

 conveyed by the branches of the windpipe. In the annexed 



* Owen. 



