284 THE LARYNX. 



]age there is occasionally found a small sj'novial bursa. The thjTO- 

 hyoid membrane is thick where subcutaneous towards the middle line, 

 but at the sides becomes thin and loose, and is covered by the thyro- 

 hyoid muscles. Behind, is the epiglottis with the mucous membrane 

 of the base of the tongue, separated, however, by adipose tissue and 

 mucous glands. I'his ligament is perforated by the su])erior laryngeal 

 artery and nerve of each side. The lateral thyro-hyoid ligaments, 

 placed at the posterior limits of the thyro-hyoid membrane, are two 

 rounded yellowish cords, which pass up from the superior cornua of the 

 thyroid cartilage, to the extremities of the great coiiiua of the hyoid 

 bone. They are distinctly elastic, and frequently enclose a small oblong 

 cartilaginous nodule, which has been named cartilago iritkca : some- 

 times this nodule is bony. 



The thyroid and cricoid cartilages are connected together by a mem- 

 branous ligament and synovial articulations. The crico-thyroid 

 membrane is divisible into a mesial and two lateral pwtious. The 

 mesial ])ortion, broad below and narrow above, is a strong triangular 

 yellowish ligament, consisting chiefly of elastic tissue, and is attached 

 to the contiguous borders of the two cartilages. Its anterior surface is 

 convex, is partly covered l)y the crico-thyroid muscles, and is crossed 

 horizontally by a small anastomotic arterial arch, formed by the junc- 

 tion of the crico-thyroid branches of the right and left superior thyroid 

 arteries. The lateral portions are fixed on each side along the inner 

 edge of the upper border of the cricoid close under the mucous mem- 

 brane : they become much thinner above, where they are attached in 

 front to the middle of the angle between the ala3 of the thyroid 

 cartilage, and behind to the anterior projection of the base of the ary- 

 tenoid cartilages : the upper edges are free l)ctween those attachments 

 and form the inferior thyro-arytenoid ligaments or true vocal 

 corda. 



The cricc-thsrroid joints, between the inferior cornua of the thy- 

 roid cartilage and the sides of the cricoid, are two small but distinct 

 articulations, having each a ligamentous capsule and a synovial mem- 

 brane. The prominent oval articular surfaces of the cricoid cartilage 

 are directed ujjwards and outwards, while those of the thpoid cartilage, 

 which are slightly concave, look in the opposite direction. The cap- 

 sular fibres form a stout band behind the joint. The movement 

 allowed is of a rotatory description, the thyroid cartilage revolving on 

 its inferior cornua, and the axis of rotation passing transversely 

 through the two joints. 



The superior thyro-ary-tenoid ligaments consist of a few slight 

 fibrous fasciculi, contained within the folds of mucous membrane form- 

 ing the false vocal cords hereafter to be described, and arc fixed in 

 front to the angle between the ala3 of the thyroid cartilage, some- 

 what above its middle, and close to the attachment of the epiglottis : 

 behind, they are connected to the tubercles on the rough anterior 

 surface of the arytenoid cartilages. They are continuous above with 

 scattered fibrous bundles contained in the aryteno-epiglottidean folds. 



The crico-arytenoid joints arc surrounded by a series of thin 

 capsular filjrcs, which, together with a loose synovial membrane, serve 

 to connect the convex cllij^tical articular surfaces on the upper border 

 of the cricoid cartilage with the concave articular depressions on the 

 bases of the arytenoid cartilages. There is, moreover, a strong posterior 



