THE LARYNX. 1103 



The Thyro-hyoid Ligaments. These constitute the thyro-hyoid membrane, and 

 the middle and two lateral Uiyro-hyoid ligaments. 



The middle thyro-hyoid ligament consists of tough, yellowish fibro-elastic tissue. 

 Its lower border is attached in the thyroid notch ; its upper to the upper border of 

 the posterior surface of the body of the hyoid bone, thus passing behind its pos- 

 terior surface, and being separated from it by a synovial bursa (sub-hyoid bursa). 

 When the thyro-hyoid membrane is removed, the lateral borders of this ligament 

 are seen to be free. 



The tivo lateral thyro-hyoid ligaments are rounded elastic cords, which pass 

 between the superior cornua of the thyroid cartilage and the extremities of the 

 greater cornua of the hyoid bone. A small cartilaginous nodule (cartilago triticea), 

 sometimes bony, is frequently found in each. 



The tkyro-hyrid membrane fills in the interval between each lateral thyro- 

 hyoid ligament and the free edge of the middle one. In this situation it is made 

 up of two layers, cellular tissue externally and mucous membrane internally and, 

 just in front of the lateral ligament, its cellular layer is pierced by the superior 

 laryngeal vessels and nerve. The cellular layer is attached all the way around, 

 above to the cornua and body of the hyoid bone, and below to the entire upper 

 border, incisura as well, of the thyroid cartilage. It thus passes in front of the 

 middle thyro-hyoid ligament, and here forms the anterior wall of the sub-hyoid 

 bursa. A*t the free edge of the middle ligament the mucous membrane passes 

 behind the epiglottis ; at the lateral ligament it is reflected on to the posterior 

 wall of the pharynx. 



The hyo-epigiottic ligament is a fibrous band, which extends from the anterior 

 surface of the epiglottis to the upper border of the body of the hyoid bone. The 

 thyro-epiglottic ligament connects the apex of the epiglottis with the receding angle 

 of the thyroid cartilage just beneath the median notch. 



The Crico-thyro-arytenoid Ligament. This is a strong fibrous lamina, bent on 

 itself anteriorly. Its attachments are as follows : (1) Posteriorly, it is attached to the 

 vocal process of one arytenoid cartilage, whence it extends as &free edge in a prac- 

 tically straight line, forward and a little inward, to the posterior aspect of the angle 

 between the alae of the thyroid cartilage. Here it bends on itself at an acute 

 angle, is attached to the thyroid, and passes backward and a little outward, as a 

 second free edge, to be attached to the vocal process of the other arytenoid carti- 

 lage. (2) From these two free edges, as an upper limit, the lamina passes down- 

 ward, with an outward slope, to the curved sloping upper border of the cricoid 

 cartilage which lies anterior to the lamina of the same, and becomes attached to it 

 in its entire extent. The ligament, as a whole, is thus seen to be V-shaped above, 

 apex forward, but of a curved outline below. Furthermore, its vertical diameter 

 varies, being smallest behind and greatest in front at the middle line, this variation 

 being due to the upper border of the cricoid, which slopes upward posteriorly until 

 it almost reaches the vocal process of the arytenoid. 



In the middle line the angle which is formed in front by the bending on itself 

 of this ligament is acute above, but obtuse or "rounded" below. The upper part 

 of this " angle " lies behind and attached to the angle of the thyroid cartilage, its 

 upper limit (i. e. the angle of the free edges) being at some distance (almost half- 

 way up) from the lower edge of the cartilage. The lower or " rounded " part is 

 the direct continuation downward of the upper, and passes to the middle of the 

 upper border of the cricoid. This last is known as the crico-thyroid membrane, is 

 subcutaneous, and is crossed by a small anastomotic arterial arch from the two 

 crico-thyroid arteries. 



Latt'i'iiH.}!* there is a considerable interval between the outer surface of this liga- 

 ment and the inner surface of the corresponding half of the thyroid cartilage, which 

 is filled in by the Thyro-arytenoid and Lateral crico-arytenoid muscles. 



The upper free edges of this ligament are thicker than the remainder, and are 

 known as the inferior thyro-arytenoid ligaments. When covered with mucous mem- 

 brane they constitute the true vocal cords. The inner surfaces of the crico-thyro- 



