386 



ZOOLCX^T 



enlarged and occupy great spaces of the body and even com- 

 municate with the cavities of the t)ones. These air-sacs serve 

 not only to diminish the sijccific gravity of the body, Ijut also 

 as reservoirs to receive the tidal air. From these reservoirs 



some of the air is no 

 doubt absorbed by 

 the l)lood and other 

 fluids of the body; 

 but the reservoirs 

 are jieriodically 

 emptied through the 

 air-tube, as are the 

 terminal sacs in our 

 own lungs. 



Organs and Func- 

 tions of Circula- 

 tion. — The heart is 

 completely divided 

 into a right and a 

 left side, as in man. 

 Each side has a re- 

 ceiving chamber or 

 auricle, and a dis- 

 charging chamber or 

 ventricle.' The im- 

 pure blood from the tissues is received l\v the right auricle, 

 passes to the right ventricle, and thence is pumped into 

 a pairerl pulmonary' artery, of which one branch goes to 

 each lung, wIktc it l)reaks up into capillaries. The re- 

 collected, oxygenated blood is returned to the left auricle, 



1 Fig. 354. 



Fig. .3.5.5. — The lungs of the pigeon, togetlier 

 with the lower end of the traehea, viewed from 

 the ventral side ; tr, trachea with the syrinx 

 (sy) at its lower end where the two bronchii (hr) 

 branch off, eventually dividing into branches. 

 br', hr" . The pulmonary arter>' enters at 

 p. a, and the vein leaves at ji.v. "With the 

 lungs, various air sacs are connected at a. in, 

 the anterior thoracic; at p. in. the posterior 

 thoracic ; at /). the abdominal ; at !<lij:, the 

 interclavicular, and at np.h, the cervical. From 

 Parker's "Zootomy." 



