LARYNX. 237 



root of the lung. Within the lung it forms interlobular septa, and the thin 

 interalveolar layers, but it is most conspicuous around the bronchi. In the 

 following sections the structure of the respiratory tract will be considered 

 beginning with the larynx, and proceeding posteriorly. 



LARYNX. 



The mucous membrane of the larynx is a continuation of that of the 

 pharynx, and likewise consists of an epithelium and tunica propria. A 

 submucosa connects it with the underlying parts. In most places the 

 epithelium appears to be stratified and columnar, but it is said to be pseudo- 

 stratified, with nuclei at several levels. It is difficult to determine whether 

 or not all of the cells are in contact with the basement membrane. This 

 type of epithelium, which occurs also in the trachea, is ciliated. The 

 stroke of the cilia is toward the pharynx. A stratified epithelium with 

 squamous, non-ciliated outer cells is found on the vocal folds [true vocal 

 cords], the anterior surface of the arytaenoid cartilages and the laryngeal 

 surface of the epiglottis. The distribution of the two sorts of epithelium 

 anterior to the vocal folds is subject to individual variation. The squamous 

 epithelium often occurs in islands. The tunica propria consists of numer- 

 ous elastic fibers and fibrillar connective tissue, which in the lower animals 

 forms a dense membrana propria under the epithelium. It also includes 

 reticular tissue containing a variable number of leucocytes; solitary nodules 

 may be found in the ventricle of the larynx [sinus of Morgagni]. Pap- 

 illae in the tunica propria are chiefly in the region of the squamous epi- 

 thelium. At the free border and on the under surface of the vocal folds, 

 the papillae unite to form longitudinal ridges. On the laryngeal surface 

 of the epiglottis there are only isolated papillae, against which rest the 

 short taste buds. 



The submucosa contains mixed, branched, tubulo-alveolar glands, 

 measuring from 0.2 to i.o mm.; they are abundant in the ventricle but are 

 absent from the middle part of the free border of the vocal folds. 



The cartilages of the larynx are mostly of the hyaline variety, resem- 

 bling those of the ribs. To this class belong the thyreoid, cricoid, the greater 

 part of the arytaenoid, and often the small triticeous cartilages. Elastic 

 cartilage is found in the entire epiglottis, the cuneiform and corniculate 

 cartilages, the apex and vocal process of the arytaenoids, and generally the 

 median part of the thyreoid. In women this portion is not involved in the 

 ossification (chiefly endochondral) which begins in the thyreoid and cricoid 

 cartilages between the twentieth and thirtieth years. The triticeous carti- 

 lages (nodules in the lateral hyothyreoid ligaments, named from their 

 resemblance to grains of wheat) are sometimes composed of fibro-cartilage. 



