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



tilage being on the under surface of the muscular process, which is pro- 

 jected backwards from the cartilage, the surfaces of attachment of 

 the muscle lie in front of the joint, i.e., in front of the fulcrum, so that 

 the muscle powerfully rotates the cartilages inwards, draws them 

 together, apposes their internal surfaces, and pulls them powerfully 

 together. Thus the muscle acts with the thyro-arytenoids as a 

 sphincter of the larynx. The muscle likewise forms an elastic liga- 

 ment between the two cartilages, fibrous tissues being clearly unsuit- 

 able. White fibrous tissues would imply fixity of interval, and elastic 

 tissues would need in certain positions to be stretched by considerable 

 muscular force, while in other positions they would be lax. The muscle 

 likewise forms part of the surface over which the bolus glides in 

 deglutition, but at this time it is in contraction, and therefore firm ; 

 and, lastly, it closes in the triangular space which must always remain 

 in front of the lamina of the cricoid, even when the arytenoids are 

 applied to one another by their inner faces. 



The Ary-epiglottic Muscle, including the Oblique Portion of the 

 Arytenoid Muscle. Its function, apparently, is to make tense the ary- 

 epiglottio folds of mucous membrane, part of the immediate bound- 

 aries of the entrance. Thus the entrance is bounded during degluti- 

 tion either by cartilage or by tense muscle, so that the bolus has no 

 chance of entering. The tension is manifest from the more marked 

 backward curvature of the lateral edge of the epiglottis; thus the 

 concavity of the epiglottis becomes more marked, forms, indeed, a 

 deeper groove to receive the tips of the arytenoids during deglutition. 

 On this account the transverse limb of the fissure, or head of the 

 ~]~, is markedly concave backwards. 



That the muscle is prolonged over the back of the upper part of 

 the cartilage of its own side to the base of the cartilage of the 

 opposite side is necessary. It thus tends to brace together the two 

 cartilages, whereas, if it only went to the cartilage of its own side, it 

 would tend to separate the cartilages, and thus to destroy the effec- 

 tiveness of the closure of the orifice. 



A subsidiary effect is to help the thyro-arytenoid in rotating 

 inwards and pulling forwards the arytenoids ; to this extent there- 

 fore, but only to this extent, is the name " constrictor vestibuli " 

 (Luschka) justifiable. 



The Lateral Crico- arytenoid Muscle. Besides rotating the arytenoid 

 cartilage, this muscle must also help in tilting the whole cartilage 

 forwards by pulling the base forwards so that the posterior part of 

 the articular surface comes to rest on the cricoid. Both this muscle 

 and the posterior crico- arytenoid being inserted at the base of the 

 cartilage, therefore very close to the axis of rotation, secure a com- 

 paratively large movement with but little actual shortening of the 

 muscles. 



