326 Mr Willis on the 



and windpipe, called the mesial plane, dividing the head sym- 

 metrically, DEFG being the external outline of the throat, 

 and H the back of the tongue. Fig. 1 is a section made by 

 a plane perpendicular to the former, and passing along the line 

 ABC. 



From A to D (Fig. 2) the windpipe presents a horizontal 

 section nearly circular; above D it contracts in the transverse di- 

 mension, assuming the form of a narrow slit, termed the glottis. 

 (The line GG (Fig. 1.) passes through the glottis). Immediately 

 above it the windpipe expands into a pair of cavities, termed the 

 ventricles of the Larynx, through which the line VV passes, and 

 above these the passage again narrows into another slit indicated 

 by the line LL, which has been termed the pseudo glottis. Above 

 this the passage again expands, and finally opens into the pharynx, 

 as the cavity behind the tongue is termed. 



The whole surface of the cavity we have been describing is 

 lined with a soft mucous membrane, similar to that which is seen 

 on the inside of the mouth, soft palate, &c, with the exception of 

 the edges of the glottis, where the lining assumes the form of a 

 ligament, white, fibrous, and elastic, the outline of which is seen 

 in Fig. 2, immediately below the opening of the ventricle. The 

 edges of the pseudo glottis are formed merely by a kind of redu- 

 plication of the ordinary mucous membrane. It will be seen from 

 Fig. 2, that neither the ligaments nor the ventricles extend entirely 

 across the passage. 



The most generally received opinion, and that which appears 

 to me to be borne out by a careful investigation of the structure 

 of the Larynx, is that the current of air from the lungs excites 

 these ligaments to vibration, and so produces the sounds of the 

 voice (vide note /I). Hence they are denominated the vocal liga- 



