SPEECH 311 



6.— SPEECH 



A sound has three quahties : pitch, which depends upon 

 the frequency of vibration ; intensity, which depends upon 

 the ampUtude of vibration ; and timbre or quahty, which 

 depends upon the relative proportions of the overtones. 



The voice is produced by the vibration of the true vocal cords 

 caused by the blast of air which is driven against them in expira- 

 tion. The vocal cords are two parallel elastic membranes covered 

 with mucous membrane and forming ridges which stretch between 

 the thyroid cartilages in front and the anterior end of the arytajnoid 

 cartilages behind, the two cartilages being separated by a cleft, the 

 rinia glottidis. Tiie arytsenoid cartilages are capable of rotation on a 

 vertical axis. 



The size of the rima can be varied by approximating or drawing 

 apart the posterior ends of the vocal cords. These movements are 

 effected by adductor and abductor muscles respectively. 



The principal abductors are the posterior crico-arytanioids, 

 which, arising from the posterior siu-face of the cricoid cartilage, 

 pass upwards and outwards to be inserted into the outer angle of 

 the arytsenoid cartilages. 



The chief adductors are the arytsenoid muscles which pass from 

 one arytsenoid cartilage to the other, and the lateral cricoarytsenoid 

 which pass from the upper border of the cricoid to the outer angle 

 of the arytajnoid. 



The cords are put on the stretch by the cricothyroid muscle 

 which passes from the cricoid cartilage to the inferior border of 

 the thyroid cartilage. When it contracts the anterior part of the 

 cricoid is drawn up and the posterior part drawn down. 



The cords are relaxed by the thyi-o-arytasnoid muscles which run 

 from the thyroid cartilage to the outer border of the arytsenoids, 

 drawing the latter cartilages forward and also approximating the 

 cords. Some of the fibres, forming a separate portion {musculus 

 vocalis), are inserted into the cord itself. This has the effect of 

 shortening the cords, and probably allows a part only of the cords 

 to vibrate. 



The fundamental note of a vocal sound depends upon the tension 

 of the vocal cords. The quality of the sound depends upon the 

 combination of overtones imposed upon the fundamental note by 

 the resonance of the air passages. These include the pharynx, 

 nasal cavity, laryngeal cavity, the cranial air-sinuses, and the 

 trachea. The variations in quality are produced by alterations in 



