148 ESSENTIALS OF PHYSIOLOGY. 



to localise the direction of a sound, and a blindfolded person has great 

 difficulty in forming a judgment as to the source of a brief sound 

 produced in line with the mesial plane of his bod} 7 . 



VOICE AND SPEECH. 



Voice is a musical note produced by the vibration of the vocal cords 

 of the larynx and modified in character by the resonating chambers 

 formed by the upper respiratory passages, the mouth, the accessory 

 sinuses of the nose, and the chest. The vocal cords are thrown into 

 vibration by expiratory currents of air from the lungs. 



The framework of the larynx is formed of cartilages connected by 

 fibrous tissue. The cricoid cartilage, resembling a signet ring in shape, 

 is connected with the upper cartilage of the trachea by a fibrous 

 membrane ; the broad part of the cartilage is situated posteriorly. 

 The thyroid cartilage is formed of two laminae which join in the middle 

 line anteriorly and are separate behind. The lower part of the posterior 

 border of each lamina articulates with the outer aspect of the cricoid 

 cartilage, so that the latter rotates to a limited extent on the thyroid. 

 The arytenoid cartilages, right and left, are pyramidal in shape, the base 

 of each articulating with a facet on the upper border of the posterior 

 portion of the cricoid. The corniculate cartilages are small, and 

 articulate with the apices of the arytenoid cartilages. The cuneiform 

 cartilages are elongated in shape and lie in the aryepiglottic folds. The 

 epiglottis is leaf-shaped, the stalk being attached to the recess of the 

 thyroid cartilage, and the flattened portion extending nearly vertically 

 upwards. 



The thyroid and cricoid cartilages and the greater part of each 

 arytenoid consist of hyaline cartilage. The apical parts of the arytenoids, 

 the. corniculate cartilages, the cuneiform cartilages, and the epiglottis 

 consist of yellow elastic fibro-cartilage. 



The lining membrane of the larynx is thrown into two antero- 

 posterior horizontal folds from the recess of the thyroid cartilage in 

 front to the anterior or vocal process of the base of each arytenoid 

 cartilage behind. These are known as the vocal cords (vocal folds), and 

 the slit which they bound is called the glottis (fig. 47). At a slightly 

 higher level there are two parallel folds, the false vocal cords (ventricular 

 folds). The recess between the true and false vocal cords is called the 

 ventricle. 



The mucous membrane of the larynx is lined by columnar ciliated 

 epithelium, but the anterior surface and upper half of the posterior 

 surface of the epiglottis, the vocal cords, and scattered patches of the 



