1892.J On the Mechanism of the Closure of the Larynx. 33 1 



less in position, the arytenoid portion is only there (luring closure of 

 the laryngeal aperture, and the lamina of the cricoid is heaved 

 forwards only during deglutition. Thus only during deglutition does 

 the lamina of the cricoid form the inferior part of the anterior wall 

 of a funnel. 



Very much the same condition of parts is seen in Manatus (Wal- 

 deyer, ' Sitzungsb. der Konig. Preuss. Akad.,' Berlin, 1886). "Here 

 one cannot speak of a bifurcation of the food channel as if it went to 

 the right and left of the epiglottis, for, in Manatus, even small quan- 

 tities of fluids must reach the oesophagus by passing straight over 

 the larynx. Since, however, the laryngeal entrance is firmly closed 

 in the way I have described, and so makes a surface gently inclined 

 backwards, the entrance of liquids and solid foods is efficiently 

 prevented." 



The two funnels then, the air-funnel and the food-funnel, are 

 alternately conditioned, the former solely, the latter largely, by the 

 movement of the arytenoid flap backwards and forwards respectively. 



In passing and in this connexion, one may point out a part played 

 by the lamina of the cricoid. When the arytenoid s move forwards 

 their vocal processes move towards each other and at the same 

 lime downwards, so that the plane of the glottis, comes to lie 

 lower posteriorly. Anteriorly, of course, the plane is fixed by the 

 attachment of the true cords to the thyroid cartilage. Thus the 

 special vocal apparatus during deglutition lies deep down within the 

 laryngeal cavity, and by the lamina of the cricoid is protected from 

 the pressure of the bolus, pulled forwards, as it is, by the muscular 

 slings of the inferior constrictor of the pharynx. 



If we think of the old descriptions of the closure of the laryngeal 

 entrance by the folding back of the epiglottis, we see at once that 

 there would be a most awkward angle round which the bolus would 

 have to travel just as it entered the gullet. This angle would be 

 formed above by the tip of the epiglottis, and below by the posterior 

 margin of the laryngeal entrance, i.e., the tip of the arytenoid flap. 

 A similar angle would exist in the case of all animals the plane of 

 the entrance to whose larynx crossed the axis of movement of the 

 descending bolus, the angle being the more marked the more nearly 

 at a right angle this plane crossed this axis, and it is partly to get rid 

 of this angle that the folding forwards of this arytenoid flap takes 

 place. In animals, on the other hand, where the ,plane and the axis 

 are parallel there is no angle and there is no folding forward of the 

 arytenoid merely an outwards and inwards movement, an opening 

 and shutting of the lozenge-shaped entrance, as in the case of the 

 Tortoise, Lizard, Frog, Snake, &c. In addition to the above angle, there 

 would be also an inconvenient open angle between the tongue and the 

 -epiglottis, in which food particles would be most likely to lodge, and 



