206 Mr. Bishop's Experimental Researches into 



cartilaTCS and internal mechanism of the larynx. The mus- 

 cles which elevate the larynx are the27/^?o-, Mylo-, Genio-, and 

 Stylo-Hyoidei, aided by the Digastrici. In this elevation the 

 Genio-glossi, the Lingualis, the Stijlo-, Thyro-*, Crico-* Pha- 

 ryngei, and the Hyu-glossi concur. 



The muscles which have an opposite effect, and lotaer the 

 larynx, are the Sterjio-Thyroidei, the Ster7io-Hyoidci, and the 

 Omo-Hyoidei. 



The second set of muscles exerts a very important influence 

 on the voice, the functions of which being imperfectly under- 

 stood will require a few details. 



The crico-thyroideus t muscle approximates the cricoid to 

 the thyroid cartilage anteriorly, and closes the chink between 

 them ; in this action, the posterior and upper edge of the cri- 

 coid is rotated backwards, by which the antero-posterior di- 

 ameter of the larynx is enlarged, and the tension of the vocal 

 ligaments increased. 



The crico-arytenoideus posticus % is situated on the posterior 

 broad surface of the cricoid cartilage, from whence it originates. 

 Its fibres, ascending obliquely outwards, are attached to the 

 base of the cricoid cartilage, between the crico-arytenoideus 

 lateralis and the arytenoideus ohliquus and transversus. This 

 muscle, by drawing the arytenoid cartilage backwards and 

 rotating it outwards, opens the aperture of the glottis. 



The crico-arytenoideus lateralis assists in closing the glottis. 

 The peculiarity of the action of this muscle is, that by draw- 

 ino- the external angular base of the arytenoid cartilage for- 

 wards, its anterior pyramidal projection, to which the vocal 

 cords are attached, is" at the same time rotated inwards. 



The thyro-arytenoideus is the most complicated, most im- 

 portant, and the least understood of any of the whole set. it 

 forms the whole superior and inferior lateral boundaiy of the 

 glottis, and is closely connected with the vocal ligaments ; its 

 direct force is to antagonize the crico-thyroidms, to rotate the 

 cricoid on the thyroid, and to draw forwards and approximate 

 the arytenoids anteriorly, as likewise to relax the vocal liga- 

 ments. The thickness of this muscle being increased and ro- 

 tated upon itself inwards when contracting, forces the edges 

 of the glottis together at its central part. By the various mo- 

 tions of the thyro-arytenoidei muscles on the vocal ligaments 

 their edges are turned into \}nQ vibrating position, and by their 

 action, in conjunction with that of their antagonists the crico- 

 thyroidei, the tension, and the vibrating length of the glottis ate 



• Names given to some fibres of the Constrictor Pharyngeus inferior, 

 t Fig. 7. : I'^ig- 2. 



