IX 



RESPIRATORY MOVEMENTS 



143 



escape in one way only, viz., through the glottis into 

 the lungs. 



Thus inspiration, or breathing-in, is produced by the 

 buccal cavity acting as a force-pump ; the lowering of its 

 floor draws in air through the nostrils, the raising of 

 its floor forces the imprisoned air into the lungs. 



^ 



ln 



FIG. 45. Diagrams illustrating the respiratory movements of the Frog ( X 2). In A 

 the floor of the mouth is depressed and air is being drawn in through the nostrils ; 

 in B the floor of the mouth is raised, the nostrils are closed, and air is being 

 forced into the lungs. 



e. n. external nostril; g/. glottis ; gul. gullet ; i. n. internal nostril; Ing. lung; 

 olf. s. olfactory sac ; pmx. premaxilla ; tng. tongue. 



Expiration, or breathing-out, is due to a contraction of 

 the elastic lungs, accompanied by a slight lowering 

 of the tip of the lower jaw : the latter movement 

 releases the premaxillae and thus opens the external 

 nostrils. 

 Respiration. By the alternate movements of inspira* 



