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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



the epiglottis. The epiglottis, which is extremely movable in a median plane, 

 may be tilted backward so as to close completely the entrance into the larynx. 



Functions of the Epiglottis. One 

 function of the epiglottis seems obviously 

 to serve as a cover for the superior entrance 

 of the larynx, over which it is said to shut 

 in the act of swallowing. But it is found 

 that deglutition occurs in a normal manner 

 when the epiglottis is wanting or is too small 

 to cover the aperture, the sphincter muscles 

 surrounding the latter being capable of pro- 

 tecting the larynx against the entrance of 

 foreign substances. It is held by some 

 that the epiglottis has an important influ- 

 ence in modifying the voice according as it 

 more or less completely covers the exit to 

 the column of vibrating air. It is also held 

 that the epiglottis acts as a sort of sounding- 

 board, taking up and reinforcing the vibra- 

 tions of the air-column impinging against it. 1 

 Sweeping downward and backward from 

 FIG. 295. vertical transverse section of each edge of the epiglottis is a sheet of 

 ^^ST^uS"^ mucous membrane, the ary-epiglottic fold, 

 epigiottic fold ; 3, ventricular band, or false which forms the lateral rim of the superior 



vocal cord; 4, true vocal cord; 5, central _ , , , , . , , . 



fossa of Merkei; 6, ventricle of larynx, with aperture of the larynx and which ends in, 

 6', its ascending pouch; 7, anterior portion an( j covers posteriorly, the arytenoid carti- 



of cricoid ; 8, section of cricoid ; 9, thyroid, ,-,, -IT ,1 



The rounded prominence on the pos- 



14 



cut surface ; 10, thyro-hyoid membrane ; 11, 



thyro-hyoid muscle; 12, aryteno-epigiottic ter i O r corner of this fold is made by the car- 



muscle; 13, thyro-ary tenoid muscle, with 



13', its inner division, contained in the vocal tilage of Santorini, and a second, less marked, 

 p^rtio^onarynx Hk cavityof thetrachea! swelling external to it, by the cartilage of 



Wrisberg (Fig. 302). Looking down into 



the larynx, it is seen that its lateral walls approach each other by the develop- 

 ment on each side of a permanent ridge of mucous membrane, known as the 

 ventricular band or false vocal cord (Fig. 295). 



Ventricular Bands and Ventricles of Morgagni. The ventricular bands 

 or false vocal cords arise from the thyroid cartilage near the median line, a 

 short distance above the origin of the true cords. They are inserted into the 

 arytenoid cartilages somewhat below the apices of the latter. Their free bor- 

 der is more or less ligamentous in structure. They are brought into contact 

 by the sphincter muscles of the larynx, and thus protect the glottis. It has 

 even been stated that, in paralysis of the true cords, they may be set in vibra- 

 tion and be the seat of voice-formation. So-called " oedema of the glottis " is 

 chiefly due to accumulation of fluid in the wide lymph-spaces found in the 

 false cords. 



1 Mills: Journ. of Physiology, 1883, vol. iv. p. 135. 



