1892.] On the Mechanism of the Closure of the Larynx. 325 



2. A series of healthy persons examined laryngoscopically. 



3. Frogs, Tortoises, Lizards, Birds, examined by simply opening the 

 mouth and observing the top of the larynx, and the effects of stimu- 

 lating certain of its muscles. 



4. The Opossum, Cat, Dog, and Goat, anaesthetised with chloroform, 

 and the laryngeal aperture examined through an incision in the 

 middle line above the level of the epiglottis. Swallowing was 

 observed as it occurred spontaneously or was evoked by irritating the 

 pharyngeal mucous membrane. The relation of the tip of the 

 epiglottis to the lower end of the incision formed an excellent guide 

 as to whether or not the epiglottis moved. The complete closure of 

 the larynx was tested by the stoppage of a current of air sucked 

 down through the larynx. 



In Man, and presumably in other animals with iarynges of a like 

 build, during respiration the arytenoid cartilages stand backwards 

 and are rotated outwards. They, surmounted by the Santorinian 

 cartilages and enveloped in the mucous membrane, are continually 

 but somewhat irregularly advancing and retiring synchronously with 

 the movements of expiration and inspiration. When they are bac^- 

 vvards as in inspiration, the arytenoids, the posterior margin of the 

 superior aperture of the larynx, lie against, and may indent, the pos- 

 terior wall of the pharynx. In forced respiration these movements are 

 exaggerated. The upward and backward direction continues more 

 or less the direction of the plane of the lamina of the cricoid cartilage. 



When the laryngeal entrance is to be closed, the arytenoid carti- 

 lages leave the posterior wall of the pharynx, are rotated and are 

 moved bodily inwards, so as to bring their internal faces into contact, 

 are inclined forwards, and glide forwards. 



By the apposition of the arytenoids a mesial fissure makes its 

 appearance, bounded posteriorly by the fold of mucosa containing 

 the transverse arytenoid muscle and laterally by the arytenoids. 

 The plane in which this fissure lies is, in Man in the erect posture, 

 obliquely from before downwards and backwards. This fissure ends 

 anteriorly in another fissure, which, however, is transverse ; the two 

 together constitute a triradiate fissure having the form of a squat ~|~ 

 the vertical limb being somewhat short, and the transverse limb 

 rounded, owing to the pulling inwards, towards the middle line, of 

 *he margins of the epiglottis, so that the epiglottis thus forms a more 

 marked hollow to receive the tips of the arytenoids. 



The transverse fissure constituting the head of the "]" i g bounded 

 anteriorly by the epiglottis, and posteriorly by the ary-epiglottic folds. 

 The ends of this fissure are closed by the junction of the ary- 

 epiglottic folds with the margin of the epiglottis, and in the middle 

 line posteriorly it receives the posterior or inter-arytenoid limb of 

 the triradiate fissure. 



