NORMAL ANATOMY OF THE LARYNX. 



105 



trachea in conjunction with the crico- thyroid 

 muscle. The nature and position of the arti- 

 culation of the thyroid, with the cricoid, render 

 the force of this ligament of great utility and 

 importance. 



The lateral crico-thyroid ligament, lig. crico- 

 thyroid lateralc, arises immediately at the side 

 of the crico-arytenoid articulation. Some fas- 

 ciculi, according to Cruveilhier and Lauth, are 

 attached to the bases of the arytenoids, others 

 are reflected horizontally forwards to the in- 

 ferior margin of the cricoid. It is bounded 

 externally by the thyro-arytenoideus and crico- 

 arytenoideus lateralis, and lined internally by 

 tlie mucous membrane of the larynx. 



T/ie crico-arytenoid articulation. The ob- 

 lique articulating convex surface of the cricoid 

 is received in a corresponding channel or 

 groove at the base of the arytenoid cartilage. 

 The ligament arises from the cricoid, and ra- 

 diates both anteriorly and posteriorly round the 

 base of the arytenoid cartilage; a fasciculus is 

 reflected along the base of its anterior mem- 

 brane behind the attachment of the thyro-ary- 

 tenoid ligament. The crico-arytenoid liga- 

 ment is thick and strong, yet sufficiently loose 

 to permit a diversity of motion. Some anato- 

 mists divide the ligament into anterior and 

 posterior. The articulation is lined and lubri- 

 cated by a synovial membrane. 



The tln/ro-arytenoid ligaments. Syn. Chor- 

 da vacates, Ferrein. Slim inlander, Germ. 

 These ligaments, as their name implies, con- 

 nect the thyroid with the arytenoid cartilages, 

 and are instrumental in the production of voice. 

 There are on each side two vocal cords, a su- 

 perior and an inferior; the cavities between these 

 ligaments are termed the ventricles of the 

 larynx. The inferior thyro-arytenoid ligaments, 

 or, as they are often denominated, " the true 

 ligaments of the glottis," are much thicker and 

 stronger than the superior : they present the 

 form of nearly rectangular parallelograms, 

 and are stretched horizontally across the long 

 axis of the larynx, from the anterior horizontal 

 tubercle of the arytenoids, to the angle formed 

 by the junction of the wings of the thyroid (c, 

 jig. 27). On their outer side these ligaments 

 are connected with the thyro-arytenoid mus- 

 cles ; their anterior extremities are inserted into 

 the thyroid, the posterior to the arytenoid car- 

 tilages ; the internal margins are free to vibrate. 

 On exposing them by the removal of the mu- 

 cous membrane they are found less than their 

 apparent volume. Immediately after death 

 they are semi-transparent, very elastic, and 

 composed of parallel fibres. They are con- 

 nected with, and form a continuation of the 

 ligamentum crico-thyroideum lateralis (k,jig. 

 24). The length of the vocal ligaments varies 

 with the general dimensions of the larynx : in 

 the adult male they are much longer than in 

 the female. In infancy they are very short, 

 and increase from that period to the age of 

 puberty in an arithmetical ratio. Thus, if at 

 one year old their length in parts of an inch 

 is 0,2500, at five years they will be 0,3333, 

 at nine 0,4166, and at fourteen 0,4999 : these 

 are close approximations. 



The superior thyro-arytenoid ligaments or 

 superior vocal cords are, in centra-distinction 

 to the inferior, denominated (though incorrectly) 

 the false ligaments : they are of less thickness 

 and strength than the inferior ligaments, and 

 are further removed from the axis of the larynx 

 (/, fig. 24). They arise from the internal 

 angle of the thyroid, and are inserted into the 

 middle of the anterior superior prominence of 

 the arytenoid cartilages (jig. 4); they are 

 composed of a few slender fasciculi of elastic 

 fibres, approaching less nearly the mesial 

 plane than the inferior ligaments ; they appear 

 more prominent, in consequence of their form- 

 ing the roof of the ventricles. They are in the 

 same plane as the aryteno-epiglottic muscle, 

 and are connected with the fibres of the lateral 

 crico-thyroid ligaments. 



According to M. Lauth there is a connexion 

 between the crico-thyroid, the lateral crico- 

 thyroid, and tliyro-arytenoid ligaments bv three 

 fasciculi, one of which is vertical, one hori- 

 zontal, and one ascending (g, h, n, fig. 24), 

 the first of these being the crico-thyroid; the 

 second the lateral ; the third connects the thyro- 

 arytenoid with the superior thyro-aryterioid 

 ligaments, and lines the bottom of the ventricles. 

 M. Lauth considers also that the thyro-epi- 

 glottic, the hyo-epiglottic, and glosso-epiglottic 

 ligaments are composed of the same elastic 

 tissue. Mu'ller and Cruveilhier concur in these 

 views. They certainly appear of the same 

 colour and texture under the microscope, and 

 undergo the same change by exposure to the 

 atmosphere : they also possess the same cohe- 

 sive elastic properties. The strength of the 

 inferior thyro-arytenoid ligaments is so great 

 that they will tear away the cartilage to which 

 they are attached without being injured, and 

 will support the force of many pounds weight. 



Muscles. The motions of the larynx are 

 exceedingly complex, and are performed by 

 two sets of muscles, which are divided into two 

 classes: 1, the extrinsic; and, 2, the intrin- 

 sic muscles. The muscles which elevate the 

 larynx are the digastrici, stylo-hyoidei, mylo- 

 hyoidei, genio-hyoidei, and hyo-glossi, and 

 those pharyngeal muscles which are inserted 

 into the cricoid and thyroid cartilages. The 

 muscles which antagonize these and lower the 

 larynx are the sterno-hyoidei, the omo-hyoidti, 

 the sterno-thyroidei, and the thyro-hyoidei. The 

 os hyoides is the centre of motion for the action 

 of these muscles. (See NECK, MUSCLES OF 

 THE.) We shall here confine our description 

 to the 



Intrinsic muscles of the larynx, Syn. ; mus- 

 cles intrinsiques, Cruveilhier. The muscles of 

 this division comprise those acting exclusively 

 on the larynx itself. There are four pairs and 

 one single: 1, the c rico-thyroidei ; 2, the 

 crico-arytenoidei postici ; 3, crico-arytenoidei 

 laterales ; 4, tliyro-arytenoidei ; and, 5, aryte- 

 noideus, which, from a difference in the direc- 

 tion of certain of its fibres, is divided into the 

 oblique and transverse. Independently of these, 

 there are some muscular fasciculi, named the 

 thyro-epiglottidei and the aryteno-epiglottidei. 



The crico-t/iyruidei. These are very short, 



