RESPIRATION IN THE MAMMALIA. 149 



449. The Birds rank above all ihe Animal creation in 

 vital energy, as well as in muscular action. This appears 

 to be in consequence of the double effects of the respira- 

 tion, on the circulating fluid, as it passes through the lungs. 



RESPIRATION IN THE MAMMALIA. 



450. But, notwithstanding we see in the Birds a won- 

 derful adaptation of the respiratory apparatus to the wants 

 and conveniences of that order, still we shall find that the 

 construction of the pulmonary system of Man and the 

 other Mammalia, involve physiological advantages not to 

 be found in any other class of animals. 



451. The points in which this superiority exists will be 

 noticed in the progress of the description of the organs of 

 respiration in Man, to which we now proceed, and which 

 may be considered as the type of the same parts in all the 

 other Mammalia. 



452. Respiration in Man. In our own species, the 

 thorax, or chest, which contains the respiratory organs, as 

 well as all the other vital parts, is entirely surrounded by 

 a frame work of bone, so that these parts are defended 

 with great care from external injury. These bones 

 consist of the spine, the ribs, and the sternum, or breast 

 bone. 



453. Trunk of the Human Skeleton. The Trunk ol 

 the Human skeleton is represented by Fig. 95, of which 

 a is the sternum, b b the spine, and c c c c the ribs. These 

 bones, it is well known, are connected together in the 

 living system, by muscles and ligaments, and by which 

 they are moved in a slight degree in the act of respira- 

 tion. 



In what respect do the birds rank above all other animals ? What is 

 said of the perfection of the pulmonary system in man? What are the 

 parts of the human skeleton which enclose the organs of respiration? 



