246 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 and a 

 tunica propria ; beneath the latter Ijes the submucosa. 



The epithelium covering the free margins of the epiglottis 

 and partly 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 ; the true vocal cord consists of the free lateral margin of the 

 crico-thyroid ligament covered by mucous membrane ; over the 

 fibro-elastic basis of the cord stretches the mucosa clothed by strati- 

 fied squamous epithelium and re-enforced externally by the fasciculi 

 of the thyro-arytenoideus muscle. In addition, large numbers of 

 leucocytes lie scattered throughout the mucosa ; in the posterior 

 surface of the epiglottis, the false cords, and the ventricle of the 

 larynx the leucocytes are so numerous within the subepithelial tissue 



