LIGAMENTS OF THE LARYNX. 909 



is called yellow or spongy cartilage, which has little tendency to ossify. 

 The structure of all the other cartilages of the larynx resembles that of 

 the costal cartilages, like which, they are very prone to ossification as life 

 advances. 



Ligaments of the larynx. The epiglottidean ligaments and the union of 

 the cricoid cartilage with the trachea have been already mentioned : the 

 other ligaments of the larynx may be divided into thyro-hyoid, crico- 

 thyroid, and arytenoid groups. 



Thyro-hyoid ligaments. The larynx is connected with the os hyoides by 

 a broad membrane and by two round lateral ligaments. The thyro-hyoid 

 membrane, or middle thyro-hyoid ligament, is a broad, fibrous, and somewhat 

 elastic membrane, which passes up from the whole length of the superior 

 border of the thyroid cartilage to the os hyoides, where it is attached to 

 the posterior and upper margin of the obliquely inclined iuferior surface of 

 the bone. Owing to this arrangement, the top of the larynx, when drawn 

 upwards, is permitted to slip within the circumference of the hyoid bone, 

 between which and the upper part of the thyroid cartilage there is occasion- 

 ally found a small synovial bursa. The thyro-hyoid membrane is thick and 

 subcutaneous towards the middle line, but on each side becomes thin and 

 loose, and is covered by the thyro-hyoid muscles. Behind it is the epi- 

 glottis with the mucous membrane of the base of the tongue, separated, 

 however, by much adipose tissue and some glands. It is perforated by the 

 superior 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 rounded extremities 

 of the great cornua of the hyoid bone. They are distinctly elastic, and fre- 

 quently enclose a small oblong cartilaginous nodule, which has been named 

 cartilago triticea : sometimes this nodule is bony. 



Crico-thyroid ligaments. The thyroid and cricoid cartilages are connected 

 together by a membranous ligament and synovial articulations. The crwo- 

 thyroid membrane is divisible into a mesial and two lateral portions. The 

 mesial portion, broad below and narrow above, is a strong triangular yel- 

 lowish ligament, consisting chiefly of elastic tissue, and is attached to the 

 contiguous borders of the two cartilages. Its anterior surface is convex and 

 is partly covered by the crico-thyroid muscles, and is crossed horizontally by 

 a small anastomotic arterial arch, formed by the junction of the crico-thyroid 

 branches of the right and left superior thyroid arteries. The lateral por- 

 tions are fixed on each side to the inner lip of the upper border of the 

 cricoid cartilage, between the deep muscles and the mucous membrane : 

 they become much thinner as they pass upwards and backwards, and are 

 continuous with the lower margin of the inferior or true vocal cords, becom- 

 ing blended with them firmly in front. 



The crico-thyroid joints, between the inferior cornua of the thyroid carti- 

 lage and the sides of the cricoid, are two small but distinct articulations, 

 having each a ligamentous capsule and a synovial membrane. The promi- 

 nent oval articular surfaces of the cricoid cartilage are directed upwards and 

 outwards, while those of the thyroid cartilage, which are slightly concave, 

 look in the opposite direction. The capsular fibres form a stout band be- 

 hind 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. 



Arytenoid ligaments. The arytenoid cartilages are connected below with 



