THE RESPIRATORY APPARATUS IN BIRDS. 483 



IHTH able to prove that they act as antagonists to the first, by contracting during inspira- 

 tion and expanding in expiration. No doubt, at the time of tli<-eoiitru<-ti<>n of the middle 

 irs. :i Miuill quantity of tho air they conttiin is driven back into tin; anterior and 

 ; "rsui's in ]i;i.-sing across the lung; and without doubt, also, these, latter give a part 

 of thrir eontrnts t > tin 1 diaphragmatic sacs at the moment of the expansion whieh draws 

 the uir into these reservoirs. M. Suppey has also noted that these contents are always 

 formed of entirely vitiated air, while the air of the middle reservoirs has only been 

 partially respired. 



It is necessary to add that the functions of the air-sacs do not cease here ; for it has 

 been demonstrated that they exercise a very marked influence : 1, On locomotion, by 

 diminishing the \v.i-ht of the body, and, by their position, rendering equilibrium more 

 stable ; 2, On the voice, the extent and power of which they augment 



2 i -2 



