86 



A COURSE ON ZOOLOGY. 



ments, much more relaxed, and the opening between 

 them is not nearly so narrow as that between the vocal 



cords. These are the 

 ligaments, 

 the upper 



Fro. 46. 



superior 



Between 



and lower ligaments 



on each side are the 



spaces or cavities 



called the ventricles 



of the larynx. 



Mutes are persons 

 deprived of the power 

 of articulate speech 

 or of producing any 

 definite sound. This 

 infirmity may result 

 from paralysis of the 

 nerves which control 

 the movement of the 

 parts of the vocal ap- 

 paratus, but complete 

 loss of speech is of 

 rare occurrence ex- 

 cepting in cases of 

 idiocy or in those born 

 deaf. It then is caused 

 by a complete absence 

 of the sense of hearing 

 and the consequent impossibility of acquiring the princi- 

 ples of language. 



BACK VIEW OF THE LARYNX. 1, thyroid car- 

 tilage ; 2, superior horn ; 3, inferior horn ; 

 4, cricoid cartilage ; 5, crico-thyroid liga- 

 ment; 6, arytenoid cartilage; 7, promi- 

 nent external angle of the base into which 

 the crico-arytenoid muscles are inserted ; 

 8, epiglottic cartilage; 9, thyro-epiglottic 

 ligament ; 10, posterior membrane of the 

 trachea. 



