1078 THE VOICE. [BOOK m. 



cord. It is called the internal thyro-arytenoid (M. thyro-ary- 

 tenoideus internus s. M. vocalis) (Figs. 189, 190, m.th.ar.i. 

 186 A) and has by some authors been subdivided into a median 

 and lateral division. The general direction of the muscle is 



-l.cr.ar.. 



FIG. 190. THE INTERNAL THYRO-ARYTENOID MUSCLE. 



The left halves of the thyroid and cricoid have been removed so as to shew the 

 right arytenoid in position. 



Th. thyroid. Cri. cricoid. Ary. arytenoid. S. cartilage of Santorini. 

 l.cr.ar. the crico-arytenoid ligament, m.th.ar.i. the internal thyro-arytenoid 

 muscle, with c.v. the vocal cord. 



horizontally backwards, but, as in the external muscle, the con- 

 stituent bundles run in various directions and some are said 

 to end or begin in the vocal cord itself. One most important 

 action of these two muscles is undoubtedly to bring the ary- 

 tenoids nearer to the thyroid and so to slacken the vocal cords ; 

 but they produce other effects, and their contractions, especially 

 those of the external muscle, help under circumstances to bring 

 the vocal cords together and so to narrow the glottis. They also, 

 as we shall see, produce changes in the form and thickness of 

 the cords. 



Of less importance than any of the above is a small muscle 

 which starting from the processus muscularis of one arytenoid 

 passes (Fig. 188 A, m.ar.o.*) obliquely upwards towards the 

 summit of the other arytenoid, crossing its fellow obliquely at 

 the back of the transverse arytenoid muscle, which it thus par- 

 tially covers ; some of the fibres seem to end in the cartilage of 

 Santorini but most of them are continued to the thyroid, the 

 ary-epiglottic fold, and the base of the epiglottis. It is called 

 the oblique arytenoid (M. arytenoideus obliquus) or it may be 

 regarded as part of a flat, irregular muscle, the thy ro-ary-e pi- 

 glottic muscle (Fig. 186 m.th.ar.ep.). Its action is to approx- 



