DISSECTION OF THE LARYNX. 233 



tion, and presents numerous pits in which are lodged mucous glands. 

 The borders of the cartilage are convex, and they are free above, but 

 below they are enveloped by the aryteno-epiglottic folds of mucous 

 membrane. The apex is pointed, and curved forwards in the upright 

 position of the cartilage. The base of the cartilage is expanded, and 

 rests on the body of the thyroid. From each side of it an irregular bar 

 of cartilage projects horizontally backwards. The epiglottis is composed 

 of yellow, elastic, fibro- cartilage. 



ARTICULATIONS, LIGAMENTS, AND MEMBRANES OF THE LARYNX. 



Mode of Union with the Hyoid Bone. The larynx is suspended to 

 the base of the skull through the intervention of the hyoid bone, the 

 tip of the thyroid cornu (heel process) of that bone being connected by 

 ligamentous fibres (without a synovial membrane) to the so-called 

 superior cornu at the supero-posterior angle of the thyroid ala. The 

 connection between the hyoid bone and the larynx is further maintained 

 by the thyrohyoid membrane, which is attached, on the one hand, to the 

 body and thyroid cornua of the hyoid, and, on the other, to the body 

 and upper edge of each wing of the thyroid cartilage. 



Mode of Union with the Trachea. The lower edge of the cricoid 

 cartilage is connected to the first ring of the trachea by a fibro-elastic 

 membrane — the crico-tracheal ligament. 



Union of the Cricoid and Thyroid Cartilages. The postero-inferior 

 angle, or inferior cornu, of each thyroid ala is articulated to the concave 

 facet on the bezel of the cricoid in a diarthrodial joint, provided with a 

 small capsular ligament, and lined by a synovial sac. The two cartilages 

 are further united by the cricothyroid membrane. This is a fibro-elastic 

 structure consisting of a central and two lateral portions. The central 

 portion is triangular and fills up the space between the adjacent edges 

 of the right and left thyroid alas. It is attached by its sides to these 

 edges, while by its base it is inserted into the upper border of the 

 cricoid. Each lateral portion lies under cover of the laryngeal mucous 

 membrane, and is shaped somewhat like a quadrant, having an inferior 

 convex edge fixed to the margin of the cricoid in company with the 

 central portion, an anterior edge confounded with the central portion, 

 and an upper straight edge which is thin and free on the side of the 

 larynx. This upper edge is the true vocal cord ; and since its fibres are 

 attached in front to the angle of union of the thyroid alas, and posteriorly 

 to the projecting anterior angle of the base of the arytenoid, it is also 

 termed the thyro-arytenoid ligament. Vocal sounds are produced by the 

 vibration of the vocal cords. 



Movements. — The movements between the cricoid and thyroid cartil- 

 ages take place around an imaginary horizontal axis passing through 



