342 Mr Willis on the 



the current which will differ entirely in their quality from the 

 former, because the vibrating length of the ligaments will be di- 

 minished by the contact of the arytenoids, and they will beat 

 against each other during vibration. 



The approach of the cricoid D to the thyroid at E, Fig. 2, will 

 however compress the cellular tissue, &c, and tend to press toge- 

 ther the vocal ligaments and the sides of the passage below them, 

 beginning at the thyroidean extremity of the glottis, and diminish- 

 ing the vibrating portion at that extremity ; and if the tension of 

 the ligaments be increased this compression will finally close 

 the aperture in the manner described by M. Magendie. 



I have been more minute in examining the mechanical action 

 of the muscles than may at first sight have seemed necessary, 

 because for want of some such examination the greatest confusion 

 prevails in all the accounts of them. Thus, while all writers agree 

 that the cricothyroidei serve to approximate the cricoid cartilage 

 to the thyroid, either by raising the cricoid or depressing the thyroid, 

 none of them have shewn how these cartilages are to be separated 

 again, neither do they agree as to the effect of this approxima- 

 tion upon the glottis. Again, Cowper and Albinus make the thyro- 

 arytenoidei draw the arytenoids nearer together; but Sommerring 

 and Haller make them separate these cartilages ; and' Meckel and 

 others make them draw forward the arytenoids. Haller thinks 

 that they relax the vocal ligaments; Bichat that they stretch them. 

 The cricoarytenoidei laterales are stated by Cowper, Haller, and 



on a longer lever than the former: but, on the other hand, the mechanical action of the 

 former muscles to press the points V strongly into contact, by bringing XNB into a 

 straight line, receives very weak opposition from the latter muscles, which have already 

 brought ghB into a straight line; therefore the joint effect of these two pair of muscles 

 will be to press together and raise the points V. 



