MUSCLES OF THE LARYNX. 



915 



and almost horizontal ; the middle are the longest, and run obliquely ; 

 whilst the lower or external fibres are nearly vertical. 



Fig. 640. 



Fig. 640. VIEW OF THE LARYNX AND PART OF 

 THE TRACHEA FROM BEHIND, WITH THE MUS- 

 CLES DISSECTED. 



h, the body of the hyoid bone ; e, epiglottis ; 

 t, the posterior borders of the thyroid cartilage ; 

 c, the median ridge of the cricoid ; a, upper 

 part of the arytenoid ; s, placed on one of the 

 oblique fasciculi of the arytenoid muscle ; b, 

 left posterior crico-arytenoid muscle ; r, ends of 

 the incomplete cartilaginous rings of the trachea ; 

 I, fibrous membrane crossing the back of the 

 trachea ; n, muscular fibres exposed in a part. 



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 

 cornu of the thyroid cartilage, and passing 

 obliquely 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 known to be of 

 any physiological significance. (Merkel, Anat. 

 und Phys. des Menschl. t Stimm-und-Sprach- 

 organs, Leipzig, 1857; Turner in Month. Med. 

 Journal, Feb. 1860.) 



The lateral crico-arytenoid muscle, smaller than the posterior, and of an 

 oblong form, is in a great measure hidden by the ala of the thyroid carti- 

 lage. It arises from the upper border of the side of the cricoid cartilage, its 



Fig. 641, 



Fig. 641. DIAGRAMMATIC VIEW FROM ABOVE OF 

 THE DISSECTED LARYNX (after Willis). 



1, aperture of the glottis; 2, arytenoid carti- 

 3, vocal cords ; 4, posterior crico-arytenoid 

 muscles; 5, right lateral crico-arytenoid muscle, 

 that of the left side being removed ; 6, arytenoid 

 muscle ; 7, thyro-arytenoid muscle of the left 

 side, that of the right side being removed ; 8, 

 upper border of the thyroid cartilage ; 9, back of 

 the cricoid cartilage ; 13, posterior crico-arytenoid 

 ligament. 



origin extending as far back as the articular 

 surface for the arytenoid cartilage. Its 

 fibres, passing obliquely backwards and up- 

 wards, and the anterior or upper ones being 

 the longest, are attached to the external 



process or outer side of the base of the arytenoid cartilage and to the 

 adjacent part of its anterior surface, in front of the insertion of the 

 posterior crico-arytenoid muscle. 



This muscle lies in the interval between the ala of the thyroid cartilage 



3 o 2 



