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. 



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

 the floor of the mouth is depressed an'' 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 ; gl. glottis ; gu!. gullet ; i. ". internal nostril ; Ing, lung; 

 olf. $. 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- 



