162 



ELEMENTS OF MAMMALIAN ANATOMY. 



Over them course numerous thin-walled capillaries, so that 

 the carbon dioxid of the blood passes out into the air as 

 the oxygen passes into the blood. Expiration is the process 



FIG. 85. 



PHOTOGRAPH OF HUMAN HEART AND LUNGS FROM VENTRAL 



ASPECT. 

 a, aorta; t, trachea. 



of forcing the air out of the lungs which have been filled 

 by an inspiration chiefly effected by depressing the dia- 

 phragm and elevating the ribs. The two processes together 

 are spoken of as a respiration. 



PRACTICAL QUESTIONS AND SUGGESTIONS. 



i. Of what four elements are the soft parts of the body largely 

 composed? 



