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



upon the resilience of the epiglottis, being engaged between it and 

 the tongue, they would give rise to irritation. Aft a matter of fact, 

 it does sometimes happen that food gets between epiglottis and 

 tongue, but it would surely often happen if the doctrine of the lid-like 

 action of the epiglottis were true. 



By my account of the normal closure of the larynx many further 

 pcnnts in the anatomy of the larynx and many observations as to its 

 physiology now receive an explanation. Some writers have come 

 near to the truth, and of all Luschka has come nearest, many passages 

 in his writing showing that he has just failed to grasp the whole 

 meaning of what he describes. 



The External TJiyro-arytenoid Muscle. The direction of its fibres is 

 in the main from before, backwards and upwards; this is clearly the 

 direction most suited to the folding forwards of the arytenoid car- 

 tilage. Thus the origin of the muscle is in front, at the thyroid 

 cartilage as the more fixed end. The insertion of the muscle extends 

 in the vertical direction, well nigh throughout the entire length of 

 the arytenoid cartilage, so that its superior fibres have a great 

 mechanical advantage in inclining the cartilage forwards, while its 

 inferior fibres especially pnll it forwards at its base. Owing to its 

 insertion into the outer surface of the arytenoid cartilage, it tends 

 powerfully to rotate the cartilage so inwards that the internal faces 

 of the cartilages come into apposition. Thus the muscle brings about 

 three of the movements of the arytenoid cartilages that close the 

 larynx, viz., rotation inwards, inclination forwards, and gliding 

 forwards at the crico-arytenoid joint. These movements have been 

 seen experimentally upon electrical stimulation in Man.* The fourth 

 movement is the apposition of the arytenoids by the arytenoideus 

 transversus. 



The muscle thus with the transverse arytenoid forms a sphincter 

 for the larynx.f 



Having this function of the muscle in mind, one at once under- 

 stands why it is such a large muscle, why it extends vertically so far 

 beyond the level of the true cords, and in short why as viewed in a 

 vertical transverse section of the larynx it seems to have so little 

 relation to the true cords : the fact is it is (with the transverse ary- 

 tenoid muscle) the true " sphincter vestibuli," for it rotates inwards the 



* Von Ziemssen, ' Die Electricitat in der Medizin.' 



t The term " constrictor vestibuli " has already been employed, but applied to 

 the ary-epiglottic muscle, by Luschka. This manifestly is incorrect, for this muscle 

 could not constrict the vestibule, i.e., down to the level of the lower border of the 

 superior cords, hoAvever much it might constrict the entrance or aditus laryngis. 



The term ''sphincter" is applied by Henle to the aggregate of the thyro- 

 arytenoids, arytenoid and ary-epiglottic muscles, but his notion of the action of this 

 muscular mass is that the arytenoid pulls the arytenoid cartilages together, while 

 the fibres that have in the relaxed condition a bend with the concavity inwards 



