328 Prof. T. P. Anderson Stuart. [Jan. 21, 



epiglottis would lie on the tongue's surface, and be firmly pulled 

 against it, so that the bolus would have less chance of getting between 

 the epiglottis and the tongue in its passage downwards. Not all 

 animals have this muscle, but then differences in the arrangements of 

 the other parts may account for this. My experiments show that 

 writers have hitherto taken too little notice of the differences in the 

 anatomy of the larynx in different animals. These differences are 

 very considerable. 



I think we can generalise by saying that the closure of the larynx 

 is invariably effected by contact of the arytenoids with each other 

 and then contact of the two together with some part of the anterior 

 wall of the laryngeal cavity, but how this latter contact is effected 

 varies with the anatomical arrangements of the parts. 



The extent of the contact of arytenoid with arytenoid varies. It 

 may be (1) by the entire internal faces of the cartilages, (2) by an 

 area along the anterior margin only, in which case the mucosa over 

 it may be very thin and the whitish cartilage may show through, as 

 in the Koala, or (3) the cartilages, though brought together, cannot, 

 owing to their form, close the respiratory glottis (Milne Edwards). 



We may, I think, divide* arytenoids into relatively large and 

 relatively small. Then the former into relatively narrow and rela- 

 tively broad. Thus we get three groups of arytenoid cartilages, viz., 

 (1) high and narrow, (2) high and broad, (3) small. 



In the high and narrow group the arytenoids fold over into contact 

 with the front wall of the laryngeal cavity: the base of the epiglottis 

 as I have described in Man and the Goat. 



In the high and broad group, including many of the Marsupials I 

 have examined, the arytenoids move more bodily forwards into 

 contact with the base of the epiglottis, or at least the front of the 

 vestibule. 



In the group of small arytenoids, neither folding nor movement 

 bodily forwards would suffice to effect the contact, and here the lower 

 part of the epiglottis is permanently bent backwards, so that the 

 Avail of the upper and front part of the laryngeal cavity forms a little 

 hood over the vocal cords, about the posterior margin of which hood 

 the arytenoid contact takes place. In this case, therefore, the 

 epiglottic base has, as it were (permanently), gone to meet the 

 (small) arytenoids, which thus are able to effect the contact with a 

 Tninimum of movement.f 



In all cases I attach the greatest importance in effecting the 

 laryngeal closure to the contact of the larynx as a whole with the 



* Provisionally. 



t On looking over the preparations of the larynx in the Hunterian Museum, I was 

 struck with the frequency of this hooded condition of the epiglottis ; it seems 

 almost the rule. 



