290 



THE LARYNX. 



tlie middle are the longest and run obliquely ; whilst the lower or 

 external fibres are nearly vertical. 



In connection with the posterior crico-arytenoid muscle, may be mentioned an 

 occasional small slip in contact with its lower border, viz., the kerato-cricoid 

 muscle of Merkel. It is a short and slender bundle, arising from the cricoid 

 cartilage near its lower border, a little behind the inferior cemu of the thyroid 

 cartilage, and passing oljliquely outwards and upwards to be inserted into that 

 process. It usually exists on only one side. Turner found it in seven out of 

 thirty-two bodies. It is not kno^^'n to be of any physiological significance. 

 (Merkel, Anat. und Phys. des mensclil. Stimm- und Sprachorgans, Leipzig, 1857 ; 

 Turner in Month. Med. Joimial, Feb. 1860.) 



Fig. 195. The lateral crico-arytenoid 



muscle (fig. 195, /), smaller 

 than the posterior, is in a great 

 measure hidden by the ala of the 

 thyroid cartilage. , It arises from 

 the upper border of the side of 

 the cricoid cartilage, its origin 

 extending as far back as the 

 articular surface for the aryte- 

 noid. Its fibres pass backwards 

 and upwards, the anterior or 

 upper ones being the longest, 

 and are_ attached to the outer 

 side of the base of the arytenoid 

 cartilage and to the adjacent part 

 of its anterior surftice, in front 

 of the insertion of the posterior 

 crico-arytenoid. 



This niur;cle is covered inter- 

 nally by the mucous membrane, 

 and at its anterior part by the 

 upper part of the crico-thyroid 

 muscle. The upper part is in 

 close contact and indeed is 

 sometimes blended with the thyro- 

 arytenoid. 



The tliyro-arytenoid muscle 

 is situated above the lateral crico- 

 arytenoid. It is thick below and 

 in front, and becomes thinner 

 above and behind. It consists 

 of several distinct fasciculi, 

 Avhicli arise in front from the 

 internal surface of the thyroid 

 cartilage, the lower two-thirds, 

 close to the angle formed by 

 the junction of the two ate, 

 and extend almost horizontally 

 backwards and outwards to 

 j-each the base of the arytenoid cartilage. The lower portion of 

 the muscle (fig. 195 d), which forms a thick fasciculus, receives a few 

 additional fibres from the posterior surface of the crico-thyroid mem- 



Fig. 195. — Side View of the Larynx 



AFTEK REMOVAL OP THE LEFT ALA OF THE 



Thyroid Cartilage (Bishop). 



The upper tliiu part of the left thyro- 

 ai7teuoid muscle has been removed to show 

 the lower part, d, supporting the vocal 

 cord, c ; a, inner surface of right ala of 

 thyroid ; h, b, arytenoid cartilages ; d', the 

 small tliyro-avytenoid muscle of Scemmerring 

 sometimes present ; c, ijosterior, and /, 

 lateral crico-firytenoid muscles of the left 

 .side ; n, cricoid cartilage ; /(, trachea. 



