THE LARYNX 



471 



two ill 



arytenoid cartilages. In the middle is a vertical ridge, to which the 

 n3Sophagus is united by cellular membrane, and on each side of this is a 

 hollow for the lodgment of muscles. 



The arytenoid cartilages (apyrawa, a pitcher, elSo<;, like), 

 number, are triangular in form, broad and 

 thick below, and pointed above. They 

 give attachment to the vocal chords, and 

 are the means b}'^ which these are rend- 

 ered tense or lax, open or close, by the 

 action of the muscles of the larynx. 



The epiglottis (cTrtyXwrTt?) is a carti- 

 lage of a heart shape, attached to the 

 angle between the lateral plates of the 

 thyroid cartilage. When pressed back- 

 wards, it closes the rima glottidis or 

 fissure between the vocal chords, and in 

 this way prevents the food from passing 

 into the larynx. 



By the aid of these cartilages, and 

 of the ligaments connecting them, as well 

 as by means of the muscles which move 

 them, a triangular opening called the 

 rima glottidis is formed, having its base 

 behind at the arytenoid cartilages and its 

 apex in front, below the epiglottis. The 

 sides of this opening are formed by liga- 

 mentous bands, attached to the arytenoid 

 cartilages, so that as these are drawn 

 backwards they are rendered tense ; and 

 if they are drawn apart the rima or 

 fissure is widened and admits more air. 

 When this fissure is contracted, either 

 by thickening of the edges or by the 

 wasting of the muscles which keep it 

 open, roaring or whistling is produced ; 

 so that it is important to arrive at 



Fig. 74.— Posterior View of the os Hyoides 

 AND Larynx. 



1. Epiglottis. 



2. Arytenoid cartilages. 



3. Cricoid cartilage. 



4. Simr process, or appendix of the os hyoides. 



5. 5. Branches of the body of the os hyoides. 



6. G. Shorthorns. 



7. 7. Long horns of the os hyoides. 



8. Membrane completing the back of the 



trachea. 



9. 9. 9. Tracheal rings incomplete behind. 

 10. 10. 10. Membrane between the rings of the 



trachea. 



correct idea of its mechanism. 



THE TRACHEA AND BRONCHI 



The TRACHEA is a flexible and elastic tube, formed of a series of incom- 

 plete cartilaginous rings, about fifty in number, connected together by an 

 elastic membrane, which also fills up the space left at the back of each 

 ring. It passes down the lower margin of the neck, and, on arriving at 

 the level of the base of the heart, it divides into two bronchi or lesser 

 tubes, of somewhat the same character and structure as itself. In its 

 course, it has the sterno-hyoideus and thyroideus in front, the oesophagus 

 behind ; and the carotid arteiy, with the pneumogastric, recurrent, and 

 sympathetic nerves on each side ; the jugular vein being more superficial 



I I 



