I2IO 



ON VOCAL SOUNDS. 



We must, however, remember that pressure of the arytenoid carti- 

 lages from behind cannot be compared accurately with the action of the 

 thyro-arytenoid muscle acting in front. The external part of the thyro- 

 arytenoid might tend to cause depression of the vocal process ; but it is 

 very difficult to see how the internal portion of that muscle can produce 

 such an effect ; and the small thyro-arytenoid of Sommering, when pre- 

 sent, will have an opposite effect. 



Many writers, while admitting that parts of the thyro-arytenoids 

 relax the cords, consider that other portions will cause increased 

 tension. 1 Jacobson, 2 who has made a careful examination of the func- 

 tion of this muscle, points out that those fibres which run from the 

 outer edge of the vocal process backwards and outwards will aid in 

 causing abduction of the cord. But we cannot admit the unqualified 

 statement that the thyro-arytenoid causes increased tension of the cords. 

 No doubt such fibres, running outwards from their insertion in the vocal 

 cords, could, by pulling on the edge and making it curved instead of 

 straight, tighten the cord. Indeed, the elliptical shape which the rima 

 glottidis assumes, after passing from the chest into the middle register, 

 may indicate some such action. If the part of the muscle which is in 

 contact with the vocal cord contracts as a whole, it will tend to make 

 the cord more rigid ; and if the arytenoids were at the same time fixed, 

 the pitch would rise. 



Voice Registers. 

 The voice has been divided into three registers, namely, the lower or 





LOWER THICK.. 



UPPER THICK. 



LOWER THIN. 





LOWER THICK. UPPER THICK.. LOWER THIN. UPPERTHIN. 



SMALL. 



Fig. 426.- 



WOMEN AND CHILDREN. 

 -Diagram showing range of registers of human voice. 



chest, the middle, and the small or head register. The average range of 

 pitch within each register is shown in the accompanying diagram 

 (Fig. 426). 



Chest register. — The chest register belongs more to the male than 



1 Foster, "Text- Book of Physiology," 1891, part 4, p. 1460. 

 " Arch. f. mikr. Anat., Bonn, 1887, Bd. xxix. 



