THE TRACHEA AND BRONCHI 



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internal laryngeal nerve is almost entirely sensor, but some motor filaments are said to be carried 

 bv it to the A/ytenoideus muscle. It divides into a branch which is distributed to both surfaces 

 of the epiglottis, a second to the arytenoepiglottic folds, and a third, the largest, which supplies 

 the mucous membrane over the back of the larynx and communicates with the recurrent laryn- 

 geal. The external laryngeal branch supplies the Cricothyroid muscle. The recurrent laryn- 

 geal passes upward under the lower border of the Inferior constrictor, and enters the larvnx 

 between the cricoid and thyroid cartilages. It supplies all the muscles of the larynx except the 

 Cricothyroid and part of the Arytenoideus. The sensor branches of the laryngeal nerves form 

 subepithelial plexuses, from which fibres ascend to end between the cells covering the mucous 

 membrane. .Sympathetic filaments accompany all of the laryngeal nerves. 



Over the posterior surface of the epiglottis, in the arytenoepiglottidean folds, and less regu- 

 larly in some other parts, taste buds, similar to those in the tongue, are found. 



Superior 



thyroid 



artery. 



Superior 

 laryngeal 

 artery. 



FIG. 890. The origin and distribution of the arteries of the larynx. (Luschka.) 



THE TRACHEA AND BRONCHI (Fig. 891). 



The trachea, or windpipe, is a cartilaginous, membranous, elastic, cylindrical 

 tube, flattened posteriorly, which extends from the lower part of the larynx, on a 

 level with the sixth cervical vertebra, to opposite the body or upper border of the 

 fifth thoracic vertebra, where it divides (bifurcatio tracheae) into two bronchi, 

 one for each lung. The trachea is nearly, but not quite, cylindrical, being flattened 

 posteriorly (Fig. 893). The largest diameter of the tube is at the middle; from this 

 point the diameter diminishes toward the bronchi and toward the laryngeal end. 

 The trachea measures about four inches and a half (11 cm.) in length; its diameter, 

 in the cadaver, from side to side is from three-quarters of an inch to an inch 

 (19 to 25 mm.), being always greater in the male than in the female. Its calibre 

 is not quite uniform throughout; the middle third is somewhat wider than the 

 rest of the tube, while just below, before its bifurcation, the trachea is slightly 

 diminished in diameter where it is in relation with the arch of the aorta. In the 

 living subject, owing to the muscle tone of the wall, the transverse diameter is 

 12.5 mm. (0.5 inch); the antero-posterior, 11 mm. (0.44 inch). 



Relations. The anterior surface of the trachea is convex, and covered in the neck, from 

 above downward, by the isthmus of the thyroid gland, the inferior thyroid veins, the arteria 



