the Physiology of the Human Voice. 207 



regulated. The thyro-arytenoideus superior serves to assist the 

 thyro-arytenoideus in relaxing the vocal ligaments. 



The arytenoideus obliquus and aryt. tra?isversus* are muscular 

 bands situated between the two arytenoid cartilages, to which 

 they are attached. Some of the fibres assume a horizontal, 

 others an oblique course, and their united action is to bring 

 these cartilages towards each other, by which the aperture of 

 the glottis is closed posteriorly. It is commonly stated in 

 anatomical works that these small muscles are capable of 

 closing the glottis, but this is incorrect. 



The lary?ix is lined throughout by a mucous membrane, 

 which being continued from the mouth, over the epiglottis, 

 forms in its descent those folds over the superior margin of the 

 thyro-arytenoidei muscles to which anatomists have o-iven the 

 name o^ pseudo-glottis; thence swelling out into a^pouch of 

 considerable size, it forms on either side the ventricle, or 

 sacculus laryngisY, and finally, after having been reflected 

 over the chorda; vocales, it passes through the cricoid cartilage 

 and becomes the membrane of the trachea. 



A number of mucous glands are situated in the folds of the 

 pseudo-glottis and in the triangular space at the base of the 

 epiglottis, their excretory ducts opening on that fibro-cartilage. 

 These glands doubtless assist in lubricating the vocal canal. 



The thyroid gland, a singular substance so named (but in 

 which no excretory duct has been discovered), is placed on 

 the larynx and superior part of the trachea; it is composed of 

 two lateral pyramidal portions, united in most subjects by a 

 distinct glandular medium. The size of this gland varies in 

 different individuals ; it is said to be larger in the female than 

 in the male. It has generally been supposd by anatomists that 

 this gland has some influence on the voice, but its true func- 

 tions are unknown %. 



The exquisite sensibility of the larynx, its dependence on 

 the will, as well as its muscular motions, are derived from the 

 superior and recurreut laryngeal filaments of the pjieumo-gastric 

 nerves. 



The distribution of these nerves to the muscles which act 

 on the glottis is a subject of anatomical controversy. Experi- 

 ments made on them by Martin ||, Professor Sue of Paris, Dr. 



• Fig. .3. 



t The sacculus laryngis insulates superiorly the vocal ligaments. 



: It appears to nic by no means impossible that the thyrSid gland secretes 

 a fluid transmitted by an invisible j-rocess which lubricates the vocal tube 

 J he constant passage of air must render it requisite to be kept permanentlv 

 moibtcned. ' 



II Edinburgh Essays. 



