638 THE VALVULAR ACTION OF THE LARYNX. 



approximation of true and false cords in the cat, at the same 

 time, variations from 30 to 60 mm. were registered. The 

 former figure is, however, the more exact, though, if there he a 

 slight increase of lateral pressure, and the epiglottis he pushed 

 gently backwards over the glottis, a pressure of 40 and 60 mm. 

 may he obtained. 



The following figures in mm. of mercury may be taken as 

 representative of the results :— 



Blowing. Stjctioit. 



True and True False True and True False 



False alone. alone. False. alone. alone. 



30-50 4-10 24-40 60-120 60-120 2-10 



It appears from these figures that closure of the superior 

 cords did not increase the powerful resistance afforded hj the 

 inferior to the ingress of air as represented by suction. A 

 quick, powerful suction (i.e., inspiration) movement closes the 

 true cords, but this does not affect the false cords in the same 

 manner, nor does the negative pressure in the trachea extend 

 to them. The larynx again tends to pass downwards, and the 

 " telescoping " due on the one hand to the elevation of the 

 larynx, and on the other to the pressing backwards of the root 

 of the tongue and of the epiglottis with its supporting pad, 

 which occurs in efforts to vomit, is here entirely absent. 



We could, however, imagine that the ventricle becoming dis- 

 tended in expiration after narrowing of the larynx by muscular 

 action and approximation of the false cords, the inferior might 

 themselves be closed by the pressure from above, and that thus 

 a slight measure of support might be afforded. 



The false cords in the dog are inconspicuous and weak in 

 comparison with the broad well- developed true cords. 



They offer almost no resistance to the ingress of air : 4 mm. 

 of mercury being the utmost, and this amount is only reached 

 when sticky mucus on the bands adds to the resistance. 



The true cords, either alone or with the false cords, resist the 

 ingress of air with a force of 80 to 180 mm. of mercury. 



The true cords alone offer a resistance of only about 9 mm. to 

 the exit of air. 



