THE NECK 155 



From the upper and lower extremities of the posterior border of each lamina 

 the superior and inferior cornua project. The latter articulates with the side 

 of the cricoid cartilage by means of a diarthrodial joint. 



The Cricoid cartilage is narrow in front, but it is much deeper posteriorly, 

 and helps to fill in the gap caused by the wide separation of the laminae 

 of the thyreoid cartilage. This gap is still further diminished by the two 

 Arytenoid cartilages, which are situated on the upper border of the posterior 

 part of the cricoid. These little cartilages are pyramidal in shape, and their 

 bases articulate with the cricoid by diarthrodial joints. The anterior basal 

 angle (vocal process) projects forwards and gives attachment to the vocal 

 fold (true vocal cord), while the lateral basal angle (muscular process) receives 

 important muscular attachments. At its apex the arytenoid cartilage is 

 capped by the corniculate cartilage (of Santorini). 



The thyreo-hyoid membrane connects the upper border of the 

 thyreoid cartilage to the upper and posterior part of the hyoid 

 bone. Its superficial surface is closely applied to the thyreo- 

 hyoid muscle, while its deep surface is separated from the 

 epiglottis and the anterior wall of the laryngeal vestibule by a 

 pad of fat. A bursa is placed between the posterior surface of 

 the hyoid bone and the upper part of the thyreo-hyoid membrane 

 to facilitate the movements of swallowing, in which the thyreoid 

 cartilage ascends behind the hyoid bone. When it is enlarged 

 the bursa may be mistaken for a thyreo-glossal cyst (p. 169), 

 as it lies in the median plane, but the laryngeal lymph glands, 

 which also lie on the thyreo-hyoid membrane, and the possible 

 presence of accessory thyreoids must be borne in mind when 

 making the diagnosis. 



The conus elasticus (crico-thyreoid membrane} is attached 

 below to the upper border of the cricoid cartilage, and passes 

 upwards under cover of the lower border of the lamina of the 

 thyreoid cartilage. Its upper border is attached in front to 

 the deep surface of the thyreoid angle, and, behind, to the vocal 

 process of the arytenoid cartilage. In the rest of its extent it 

 is free and forms the vocal ligament, which is one of the important 

 constituents of the vocal fold (true vocal cord). 



The epiglottis is a leaf-shaped cartilage, which lies in the 

 anterior wall of the laryngeal vestibule. Its wide upper end is 

 free and projects above the hyoid bone in relation to the dorsum 

 of the tongue, while its narrow lower end is attached to the 

 deep surface of the thyreoid angle. Anteriorly, the epiglottis is 

 separated from the thyreo-hyoid membrane by a pad of fat, 

 and is attached by a ligament to the deep surface of the hyoid 

 bone. The mucous membrane passes from the dorsum of the 

 tongue to the front of the upper part of the epiglottis, forming 

 the floor of a depression, which is divided into two by the glosso- 



