THE RESPIRATION 



307 



abolished. The heart fails, and thus, although the arterioles 

 are still contracted, the pressure in the arteries falls. Finally 

 the movements of the heart cease and death supervenes. 



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 instrument, and it consists of a bellows, a windpipe, a 

 vibrating reed, and resonating 

 chambers. In man and other 

 mammals the bellows are formed 

 by the lungs and the thorax. 

 The trachea is the windpipe. 

 The vocal cords in the larynx 

 are the vibrating reeds, and the 

 resonating chambers are the 

 pharynx, nose, and mouth. 



A. Structure. The points of 

 physiological importance about 

 the structure of the larynx are 

 the following : 



1. Cartilages (FigS. 141, 142). FIG. 141. Side View of the Carti- 



The ring-like cricoid (Cr.) at 

 the top of the trachea is thickened 

 from below upwards at its pos- 

 terior part and carries on its 

 upper border two pyramidal car- 

 tilages 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. From their anterior angles the 

 vocal cords arise and run forward to the thyroid. The 

 thyroid cartilage (Th.) forms a large shield which articu- 

 lates by its posterior and inferior process with the sides of 

 the cricoid so that it moves round a horizontal axis. To 

 the upper and anterior part, the epiglottis or cartilaginous 

 lid of the larynx is fixed. 



2. Ligaments. The articular ligaments require no special 



Cr. 



lages of the Larynx. Cr., Cri- 

 coid Cartilage; Ar., Right 

 Arytenoid Cartilage ; Th. , Thy- 

 roid Cartilage. The dotted line 

 shows the change in the position 

 of the Thyroid by the action of 

 the Crico-thyroid Muscle. 



