300 THE RESPIRATORY SYSTEM 



structure of its mucous membrane resembles that of the Schneiderian 

 membrane, but its dorsal wall, in addition to the ciliated epithelium, the 

 thin-walled blood-vessels, and the numerous secreting glands, contains 

 many small nodules of lymphoid tissue. These nodules form a consider- 

 able mass, the pharyngeal tonsil. 



The ciliated epithelium of the nasopharynx is also continuous with 

 the lining epithelium of the auditory (Eustachian) tube. The tunica 

 propria is firmly adherent to the bony wall of the dorsal surface, but is 

 more loosely attached laterally and ventrally to the pharyngeal and 

 palatine muscles. 



THE LARYNX 



The wall of the larynx is formed by several large plates of hyaline 

 cartilage thyroid, cricoid, and arytenoid cartilages which are firmly 

 united by ligamentous bands of fibrous tissue; the cartilaginous wall in- 

 closes a mucous membrane of considerable thickness. 



The larger cartilages are of the hyaline variety and are prone to 

 ossify in adult life. The tips of the arytenoids, the cornicula of San- 

 torini, the cuneiform cartilages of Wrisberg, and the epiglottis are of 

 the elastic variety of cartilage, and, though frequently much infiltrated 

 with fat, are not, like the hyaline cartilages, subject to ossification. The 

 median portion of the thyroid cartilage is also generally elastic in char- 

 acter; this portion does not generally ossify in women. In the lateral 

 hyothyroid ligaments are the minute triticeous cartilages, generally 

 hyaline but occasionally fibrous in character. 



The intrinsic muscles of the larynx, taking origin from these car- 

 tilages, pursue their course beneath the mucous membrane. 



The upper portion of the larynx, including the greater part of the 

 epiglottis, as far as the false vocal cords is lined by stratified squamous 

 epithelium which is continuous with that of the pharynx. 



The epithelium of the vocal cords and that covering the anterior 

 surface of the arytenoids is also of the stratified squamous variety. 

 The remaining portions of the larynx, including the base of the epiglottis 

 on its laryngeal surface, the ventricle, and the entire portion below the 

 level of the true vocal cords, are lined by columnar ciliated epithelium 

 of the pseudo-stratified type. The ciliary motion is directed toward the 

 pharynx. The epithelium rests upon a basement membrane which is 

 less highly developed than in other portions of the respiratory tract. 



The tunica propria consists of fibro-elastic connective tissue in which 



