554 OF THE VOICE AND SPEECH. 



so constructed as to set it in vibration, as it passes forth from the 

 lungs. In Reptiles, the vibrating apparatus is situated at the point, 

 where the trachea opens into the front of the pharynx ; it is of very 

 simple construction, however, being only composed of a slit bounded 

 by two contractile lips ; and few of the animals of this class can pro- 

 duce any other sound than a hiss, which, owing to the great capacity 

 of their lungs, is often very much prolonged. In Birds, the situation 

 of the vocal organ is very different. The trachea opens into the front 

 of the pharynx, as in Keptiles, by a mere slit ; the borders of which 

 have no other movement than that of approaching one another, so as 

 to close the aperture when necessary. This appears to be the instru- 

 ment for regulating the ingress and egress of air, in conformity with 

 the wants of the respiratory function. The vocal larynx of Birds is 

 situated at the lower extremity of the trachea, just where it subdivides 

 into the bronchial tubes ; and it is of very complex construction, espe- 

 cially in the singing birds. In Mammalia, on the other hand, the 

 vocal organ and the regulator of the respiration are united in one la- 

 rynx, which is situated at the top of the trachea. There are few, if 

 any, of this class, which have not some vocal sound ; but the variety 

 and expressiveness which can be given to it, differ considerably in the 

 several orders ; being by far the greatest in Man, who alone, there is 

 reason to believe, has the power of producing articulate sounds, or pro- 

 per language. 



974. The Larynx is built-up, as it were, upon the Cricoid cartilage 

 (Fig. 165, x w r u), which surmounts the trachea, and which might be 



Fig. 165. 



Bird s-eye view of Larynx from above, after Willis: o E H, the thyroid cartilage, embracing the ring of 

 >id .r UTLW, and turning upon the axis x z, which passes through the lower horns; N F, N F, the ary- 

 tenoid cartilages, connected by the arytenoideus transversus ; T v, T v, the vocal ligaments; N x, the right 

 lo-arytenoideus laterahs (the left being removed); v kf, the left thyro-arytenoideus (the right being re- 

 moved); N I, N I, the cnco-arytenoidei postici; B u, the crico-arytenoid ligaments. 



considered as its highest ring modified in form, its depth from above 

 downwards being much greater posteriorly than anteriorly. This is 

 embraced, as it were, by the Thyroid cartilage (a E H) ; which is arti- 



