266 



THE VITAL FUNCTIONS. 



priated, constituting a distinct circulation. This 

 I have endeavoured to illus- 

 trate by the diagram, Fig. 

 353, where d represents the 

 auricle, and e the ventricle 

 of the heart; and a and c, 

 the main arterial and venous 

 trunks; and where the two 

 circulations are, for the sake 

 of distinctness, supposed to 

 be separated from one ano- 

 ther, so that the two systems 

 of vessels may occupy dif- 

 ferent parts of the diagram. 

 The vessels which pervade the body generally 

 (b), and are subservient to nutrition, belong to 

 what is termed the greater^ or systemic circula- 

 tion : those which circulate the blood through 

 the respiratory organs, (r), for the purpose of 

 aeration, compose the system of the lesser, or 

 respiratory circulation. 



Few subjects in Physiology present a field 

 of greater interest than the comparison of the 

 modes in which these two great functions are, 

 in all the various classes of animals, exactly 

 adjusted to each other. So intimately are the 

 organs of circulation related to those which dis- 

 tribute the blood to the respiratory organs, that 

 we never can form a clear idea of the former, 

 without a close reference to the latter of these 



