K ESP I R ATI ON I N T II B C 11 E LON 1 A 



25 



quite passively, and the Hank spaces in front of the posterior limbs sink so as to 

 present deeply concave surfaces. 



Fig. 7. 



B 







V 



Fig. 7, A. The glottis closed. — a a', the line formed by the glottic 

 lips when the animal is not breathing ; 6, the prominent 

 central part of the glottic lips, indicating the summit of the 

 arytenoid cartilage ; c, tongue ; d, lower jaw. 



Pig. 7, B. The appearance of the glottis 

 during respiration. — a, right glottic 

 lip ; b, rima glottidis ; c, extremity of 

 the hyoid bone. 



A full inspiration instantly follows. The flank spaces become flat and tense, 

 rising to a level. The glottis remains open. The hyoid arches advance, and at the 

 close of the inspiration the shoulders are pushed passively forward. 



As soon as the lungs are completely filled, a very slight expiration relieves them 

 of the surplus air, the flank spaces sinking a little, the hyoid arch at rest, the 

 glottis closing at the end of the expiration. The final action here described 

 appears to be due to the cessation of activity on the part of the inspiratory muscles 

 and to the passive falling in of the limbs displaced during their contraction. The 

 lungs are thus left full of air, and ready for the next act of respiration. "Whenever 

 a turtle in air breathes, these triple actions occur, but when under water it occa- 

 sionally expires air, and does not rise to renew the supply until some time has 

 passed by. 



Type of respiration in Ghelonia. — We arc now prepared to examine the subject 

 from another point of view. A superficial observer, or one who accepts the present 

 belief, sees in the motions of the hyoid arches a movement in appearance corres- 

 ponding to the respiratory play of the floor of the frog's mouth. Yet the slightest 

 anatomical examination should have shown that, while in the frog the nostrils have 

 valves essential to their mode of breathing, in the turtle there are none, while the form 

 of the horny lips in the latter animal renders it impossible to make the mouth so 

 air-tight as to act the part of a chamber in the supposed process of pumping air 

 into the lungs. On the other hand, the laryngeal cavity is also too small to act as a 

 chamber, nor does the hyoid arch, in its descent, enlarge the laryngeal area. 



When, at the beginning of this research, one of us observed the turtle (snapper) 

 breathing with an open mouth, while watching a chance to bite, he was at once 

 convinced that the agents of respiratory movement were below the trachea, and the 



