330 THE RESPIRATORY SYSTEM 



rise to the condition of adenoids. When the adenoids are 

 extensive, they fill up the nasal part of the pharynx and render 

 nasal breathing impossible. In addition, the pharyngeal orifice 

 of the auditory tube may become occluded, and, consequently, 

 children who suffer from adenoids not only breathe through the 

 mouth but are also dull of hearing. 



As the atmospheric air passes through the nasal cavity on 

 its way to the lungs, it absorbs a slight amount of moisture 

 from the nasal mucous membrane and its temperature is 

 slightly raised. These alterations in the character of the air 

 must be brought about also when the patient breathes through 

 the mouth, and, under these circumstances, the air absorbs 

 moisture from the mucous membrane of the tongue, which 

 becomes unpleasantly and unnaturally dry in consequence. 



THE LARYNX 



The larynx is kept constantly patent by its cartilaginous 

 walls, and it communicates with the laryngeal part of the 

 pharynx through its superior aperture. 



The thyreoid cartilage consists of two laminae which meet 

 in the median plane anteriorly and form the laryngeal promin- 

 ence (pomum Adami\ which is subcutaneous. The cricoid 

 cartilage is shaped like a signet ring. Its narrow anterior 

 part can be felt through the skin i inch below the laryngeal 

 prominence, and its deeper posterior part expands to fill up the 

 gap which exists posteriorly between the two laminae of the 

 thyreoid cartilage (Fig. 116). A small diarthrodial joint exists 

 between the inferior cornu of the thyreoid and the side of the 

 cricoid, and enables the cartilages to be moved, one on the 

 other, by the contraction of the crico-thyreoid muscles (p. 335). 



The arytsenoid cartilages, two in number, articulate with 

 the upper border of the posterior part of the cricoid cartilage. 

 They are pyramidal in shape and their anterior basal angles 

 receive the posterior attachments of the vocal folds (true 

 cords). 



