VOICE. 



In connection with the respiratory mechanism of many- 

 animals, an arrangement for the production of sound or voice 

 is developed. This is constructed on the principle of a wind 

 instrumeat, and it consists of (1) a bellows, (2) a windpipe, 

 (3) a vibrating reed, and (4) resonating chambers. In man 

 and other mammals the bellows is formed by the lungs and 

 thorax ; the windpipe is the trachea ; the vocal cords in 

 the larynx are the vibrating reeds; and the resonating 

 chambers are the pharynx, nose, and mouth. 



A. Structure of the Larynx. 

 The points of physiological importance in the structure of 

 the larynx are the following : — 



1. Cartilages (figs. 223, 224).— The ring-like cricoid (Cr.), at 

 the top of the trachea, is thickened from below upwards at 

 its posterior part and carries on its upper border two pyramidal 

 cartilages, triangular in section— the arytenoids (Ar.). These 

 articulate with the cricoid by their inner angle. At the outer 

 angle, the posterior and lateral crico-arytenoid muscles are 

 attached. The vocal cords arise from their anterior angles and 

 run forward to the thyreoid.^ The thyreoid cartilage (Th.) forms 

 a large shield, which articulates by its posterio-inferior 

 processes with the sides of the cricoid, so that it moves round a 

 horizontal axis. The epiglottis, or cartilaginous lid of the 

 larynx, is fixed to its upper and anterior part. 



2. Ligaments. — The articular ligaments require no special 

 attention. The true vocal cords are fibrous ligamentous 

 structures which run from the anterior angle of the arytenoids 

 forward to the posterior aspect of the middle of the thyreoid. 

 They contain many elastic fibres and are covered by a stratified 

 squamous epithelium, and they appear white and shining. 



The vocal cords increase in length as the larynx grows ; 

 in adult life, they are generally longer in the male than in the 



1 The name thyroid, instead of th3'reoid, is based upon a mistake ; 

 dvpeos is a shield, while dupos is a door or aperture. 



550 



