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NORMAL HISTOLOGY. 



CHAPTER XIV. 



THE RESPIRATORY ORGANS. 



THE respiratory tract consists of two parts, the system of air- 

 passages, including the nasal fossae, pharynx, larynx, trachea, and 

 bronchial tubes, and special organs, the lungs, devoted to the per- 

 formance of the respiratory function. 



THE LARYNX. 



The larynx consists of the cartilaginous framework formed by 

 the thyroid, the cricoid, the arytenoid, and the other smaller car- 

 tilages of Wrisberg and of Santorini, united by the ligamentous 

 membranes and the bands of fibrous tissue, and lined within by 

 mucous membranes ; on the outside the cartilages are covered by 

 fibrous and muscular structures. 



The mucous membrane of the larynx possesses the same con- 

 stituents as does that of the pharynx, namely, an epithelium, a tunica 

 propria, and a submucosa. 



The epithelium covering both surfa<!es of the epiglottis and the 

 cavity of the larynx as far as the false vocal cords is stratified 

 squamous in character ; at the lower edge of the false vocal mem- 

 branes the epithelium becomes stratified ciliated columnar, which 

 type is retained throughout the ventricle of the larynx. Over the 

 true vocal cords the epithelium once more becomes stratified 

 squamous, beyond which point the stratified ciliated columnar 

 character is again resumed and retained throughout the trachea 

 and the bronchi. Numerous taste-buds, identical in structure with 

 those of the tongue, lie embedded on the posterior surface of the 

 epiglottis. 



The tunica propria of the larynx is composed of fibrous connec- 

 tive tissue, with which is mingled an especially rich net-work of elastic 

 fibres ; in the true vocal cords, almost the entire membrane con- 

 sists of longitudinal bundles of elastic tissue ; these cords, therefore, 

 are folds of the mucosa, composed principally of elastic fibres, with 

 some fibrous tissue, covered by stratified squamous epithelium and 

 re-enforced externally by the fasciculi of the thyro-arytenoideus mus- 

 cle. In addition, large numbers of leucocytes lie scattered through- 

 out the mucosa ; in the posterior surface of the epiglottis, the false 

 cords, and the ventricle of the larynx the leucocytes are so numerous 



