108 



NORMAL ANATOMY OF THE LARYNX. 



corresponds with the posterior surfaces of the 

 arytenoid cartilages, and is connected by some 

 muscular fibres and membrane with the supe- 

 rior margin of the cricoid cartilage and with 

 the whole length of the internal margins of the 

 arytenoid cartilages. The immediate effect of 

 the contraction of the arytenoid muscles is to 

 approximate the posterior internal surfaces of 

 the arytenoid cartilages, but their action, at the 

 same time, tends to separate the anterior pro- 

 minences, and to open the chink of the glottis. 

 To counteract this effect the action of the crico- 

 arytenoideus lateralis is called simultaneously 

 into play, and the joint effect of these two 

 muscular forces, represented by the lines N X 

 and NY (Jig. 30,) produce a resultant in the 

 direction of W N ; hence the crico-arytenoideus 

 lateralis and the arytenoideus muscle acting 

 together tend to close the glottis posteriorly. 



The thyro-arytenoideus. This is one of 

 the most important, most complicated, and 

 perhaps least understood of any of the muscles 

 of the larynx. It arises from the side of the 

 angle of the thyroid cartilage, occupying about 

 two-thirds of its height, and reaches within 

 two or three lines of its superior margin. The 

 central fibres are directed horizontally back- 

 wards and outwards, slightly inclined upwards, 

 and inserted into the prominence and concavity 

 on the lateral surface of the arytenoidf/, Jig. 27). 

 The superior fibres terminate in the external 

 ridge of the arytenoid ; some of them pass 

 round the arytenoid, and enclose the arytenoid 

 muscle like a sphincter.* The inferior fibres 

 which arise near the median plane (k, 29) 

 are inserted, at a greater distance from it, into 

 the arytenoid cartilages (f, fig. 30) ; some ex- 

 ternal fibres are directed more eccentrically 



Fig. 29. 



Fig. 30. 



A view of the larynx from above. (From Mr. Willis.) 



The mucous membrane is removed to shew the 

 ligaments and muscles of the glottis. "N F, N F, 

 the arytenoid cartilages ; T V, the vocal ligaments ; 

 N X, the right crico-arytenoideus lateralis, the left 

 is removed ; Xt> L, the ring of the cricoid capable 

 of rotating on the axis R S ; e e, the crico-aryte- 

 noidei postici ; E, the junction of the wings of the 

 thyroid. 



Lauth, Mem. de 1'Acad. deMed. 1835. 



A portion of Jig. 29 enlarged to demonstrate the di- 

 rection and result of the forces of the muscles of the 

 larynx. 



O P, the horizontal projection of the axis of 

 articulation ; T V, the vocal ligament ; g h, the 

 direction of the force of the thyro-arytenoideus ; 

 N X, of the crico-arytenoideus lateralis; N W, 

 of the crico-arytenoideus posticus ; N Y, of the 

 arytenoideus transversus. 



upwards and backward, corresponding to the 

 superior ligaments and ventricles, where, ac- 

 cording to Lauth, they terminate without 

 reaching the arytenoid. Some fibres of the 

 thyro-arytenoid take an oblique direction back- 

 wards and downwards, arising immediately 

 below the superior internal margin of the angle 

 of the thyroid, and are inserted into the ver- 

 tical prominence of the arytenoid cartilage : 

 they are sometimes detached from those passing 

 horizontally, as in d, (fig 28,) constituting the 

 thyro-arytenoidei superiores of Albinus, but 

 they are sometimes described as one muscle. 



The thyro-arytenoideus corresponds to the 

 internal surface of the thyroid cartilage, from 

 which it is separated by some loose cellular 

 and adipose tissue. Internally it is in contact 

 with the inferior vocal ligament, which lies in 

 contact with the thickest part of this muscle, 

 the bulk of which causes the vocal ligaments 

 on each side to project towards the mesial line 

 and contracts the aperture of the larynx. Some 

 anatomists consider that the thyro-arytenoid 

 ligaments consist of nothing more than the 

 tendons of these muscles; it is not difficult, 

 however, to prove the contrary by dissection. 



The functions of the thyro-arytenoidei, con- 

 cerning which there has been much diversity of 

 opinion, produce several changes in the rela- 

 tive position of the internal mechanism of the 

 larynx, and therefore they require rigid inves- 

 tigation. The effects of these muscles may 

 be considered, first, with respect to the tension 

 of the vocal ligaments; secondly, to the aper- 

 ture of the glottis. We observe that the points 

 of attachment (at dd' I, Jig. 27) of the thyro- 

 arytenoid are situated within those at A B, 

 (Jig.28); and, as the arytenoid cartilage is tied 

 by ligamentous fibres to the point B, it follows 

 that the contraction of this muscle will draw upon 

 the point B, through the interposed arytenoid 

 cartilage : if A be made the fixed point, the 

 contraction of this muscle will draw the point 

 B towards A by rotating the cricoid on the thy- 

 roid. If, on the contrary, B be fixed, then A 

 will approach B by the rotation of the thyroid 

 on the cricoid. In both these cases the dis- 

 tance from A to B is diminished, and as the 

 vocal ligaments are situated in a direct line 



