THE EESPIKATOKY ORGANS LARYNX AND TRACHEA. 573 



This part also of the mucous membrane of the pharynx, abounds in. 

 glands. 1. Eacemose mucous glands -$ to T ' 2 of an inch in diameter, 

 form a perfectly continuous layer on the posterior wall around the 

 Eustachian tubes, and on the posterior surface of the velum. 2. Closed 

 follicular glands, simple as well as compound, are met with on the 

 vault of the pharynx, where the mucous membrane is closely attached 

 to the base of the cranium. A glandular mass extending from one 

 Eustachian opening to the other, and 1 to 4 lines thick, is constantly 

 found here. This, in aged persons, frequently presents large cavi- 

 ties filled with puriform masses. Other glands also exist upon the 

 sides of the pharynx, and on the posterior surface of the velum, 

 which probably have the same structure as the mucous sacs on the 

 base of the tongue (p. 520). 



2. The larynx and trachea, with the continuations of the latter 

 into the lungs (bronchial subdivisions), resemble in form the excre- 

 tory ducts of the compound racemose glands, which the lungs may, 

 in fact, be regarded as being. The larynx has a framework of car- 

 tilages with their connecting ligaments ; the thyroid, cricoid, and 

 two arytenoid being true (hyaline) cartilages. The epiglottis, how- 

 ever, and the cartilages of Santorini and Wrisberg, are reticular 

 cartilages (p. 314); and the cartilago triticea is common fibre-carti- 

 lage. Of the ligaments, the middle crico-thyroid, and the inferior 

 thyro-arytenoid (chordce vocales) contain a preponderance of elastic 

 fibres, and are of a yellow color. The other ligaments and the 

 hyo-thyroid membrane, also contain an abundance of this element. 

 To the cartilages and ligaments just mentioned, the striated muscles 

 of the larynx are attached; but which present nothing peculiar to 

 the histologist. 



The mucous membrane of the larynx, continuous with that of the 

 mouth and pharynx, is smooth and whitish-red, and above the 

 chordae vocales, has an abundant layer of areolar tissue under it. 

 The membrane is very closely adherent to the vocal cords, and 

 where it lines the larynx below them ; and is prolonged into its ventri- 

 cles. Its corium presents no papillae, and its outer portion abounds 

 in elastic networks. The epithelium on the epiglottis is compound 

 scaly, like that of the oral cavity. At its base and above the 

 upper vocal ligaments, commences the compound conoidal ciliated 

 epithelium, lining the air-passages throughout. It is here com- 

 posed of several layers of cells, and is 5^0 to g^ of an inch thick. 

 The external (ciliated) cells are 5 <y to ^ of an inch long, by 



