THE METABOLIC MACllINEUY OF ANIMALS ,509 



the fundamental numbcM-. An idea of the changes involved from life 

 in the water to life on land may be secured from tli(> figure. 



11 w E "2: "St 



^.^.^ ^ 



duarsoX aorta 



primitive condition 



. . r ^ventro.! aorta. 



carotid j- _ i ► 



dorsal aorta 



^ -^= ^ 



yauriclez^^^^) - . . 



-ventral aorta~ri^^ri;;^:^i 



*^T - t; — '^^\iM?lliTl Ir^l f --^ ^ Oorsol OLorto. 



'\~\^ \'\\'\ '\'\\sA^^Na\x4\\^ \V ^^^^^^ am phibian 



V ventrol oorxa 

 carotjdC left systemic arch. 



,^;^'_-'^-^ -i-"^ - - CZ;X!r ''''r^~^-"r;m^ — - ^ dorsql Op rto. 



uAV^^^^^ ^igber am phibia 

 ^_ ____^ ^ ot^ re ptiles 



'pvuTOonary trunk 



Carotid.) ri^t systemic arcVj , 



* ^ "''' rr"'-'- '\ ^ ^ '- ^ ' '^.' ■ / - - -^■■;-..-^Wx, pv.\trtort(xrir a.-rtti^y 



■ Vi /^^' ^7 — \ V, l AjT l ^^— --•^ cAorsol oiorto. 



-.;..> ,^ , ,., ^ wi^-- -'-^^i-^^^^ bird: 



^^^j;!?'^-^.. ^ S"^e^^ig!l. great a rch of oorta 



7T— '•TY'; — '■ r\\\Vl"\\/9 '"•';' ""V'"'7yf( aors-o-i aorcct 



'--■"■^"-'-:!"....i^ ^.^ '''^ ;;::_-----"'^xJpuiTnonarx tnmk 

 Fate of the aortic arches of the vertebrates as seen from the side. (After (iiiyer.) 



The Course of the Blood in the Body 



There are two distinct systems of circidation in the body. The 

 pulmonary circulation, noted in connection with the study of the 

 heart, takes blood from the right auricle and ventricle to the lungs, 

 passing it back to the left auricle. The longer circulation is known 

 as the systemic circulation in which the blood leaves the left ventricle 

 through the dorsal aorta and through ever-branching arteries pa.sses 

 to the muscles, nervous system, kidneys, skin, and other organs of 

 the body. It gives food and oxygen to these tissues, receives the 

 waste products of oxidation while passing through the microscopic 

 capillaries, and returns to the right auricle through veins. 



