1108 THE ORGANS OF VOICE AND RESPIRATION. 



encircle the superior aperture of the larynx. It lines the whole of the cavity of 

 the larynx ; forms, by its reduplication, the chief part of the superior or false 

 vocal cord ; and, from the ventricle, is continued into the sacculus larvngis. It 

 is then reflected over the true vocal cords, where it is thin and very intimately 

 adherent; covers the inner surface of the crico-thyroid membrane and cricoid 

 cartilage ; and is ultimately continuous with the lining membrane of the trachea. 

 It is covered with columnar ciliated epithelium below the superior vocal cord, 

 but above this point the cilia are found only in front, as high as the middle 

 of the epiglottis. In the rest of its extent the epithelium is of the squamous 

 variety ; as is also that covering the true vocal cords. 



Grlands. The mucous membrane of the larynx is furnished with numerous 

 muciparous glands, the orifices of which are found in nearly every part ; they 

 are very numerous upon the epiglottis, being lodged in little pits in its substance ; 

 they are also found in large numbers along the posterior margin of the aryteno- 

 epiglottidean fold, in front of the arytenoid cartilages, where they are termed the 

 arytenoid glands. They exist also in large numbers upon the inner surface of the 

 sacculus laryngis. None are found on the vocal cords. 



Vessels and Nerves. The arteries of the larynx are the laryngeal branches 

 derived from the superior and inferior thyroid. The veins accompany the arteries : 

 those accompanying the superior laryngeal artery join the superior thyroid vein 

 which opens into the internal jugular vein ; while those accompanying the inferior 

 laryngeal artery join the inferior thyroid vein which opens into the innominate 

 vein. The lymphatics terminate in the deep cervical glands. The nerves are the 

 superior laryngeal and the inferior or recurrent laryngeal branches of the pneumo- 

 gastric nerves, joined by filaments from the sympathetic. The superior laryngeal 

 nerves supply the mucous membrane of the larynx and the Crico-thyroid muscles. 

 The inferior laryngeal nerves supply the remaining muscles. The Arytenoid 

 muscle is supplied by both nerves. 



THE TRACHEA (Fig. 705). 



The Trachea, or Windpipe, is a cartilaginous and membranous cylindrical tube, 

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

 with the sixth cervical vertebra, to opposite the fourth, or sometimes the fifth, 

 dorsal, where it divides into the two bronchi, one for each lung. The trachea 

 measures about four inches and a half in length (10-11 cm.) ; its diameter, from 

 side to side, is from three-quarters of an inch to an inch (2-2J cm.), being always 

 greater in the male than in the female. 



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 thyroidea ima (when that vessel exists), the Sterno-hyoid 

 and Sterno-thyroid muscles, the cervical fascia, and more superficially, by the 

 anastomosing branches between the anterior jugular veins : in the thorax it is 

 covered from before backward by the first piece of the sternum, the remains of the 

 thymus gland, the left innominate vein, the arch of the aorta, the innominate and 

 left common carotid arteries, and the deep cardiac plexus. Posteriorly, it is in 

 relation with the oesophagus ; laterally, in the neck, it is in relation with the com- 

 mon carotid arteries, the lateral lobes of the thyroid gland, the inferior thyroid 

 arteries, and recurrent laryngeal nerves ; and in the thorax it lies in the space 

 between the pleurae (superior mediastinum) ; having the pneumogastric nerve on 

 each side of it. 



The Right Bronchus, wider, shorter, and more horizontal in direction than the 

 left, is about an inch in length, and enters the right lung opposite the fifth dorsal 

 vertebra. The vena azygos major arches over it from behind, and the right pul- 

 monary artery lies below and then in front of it. About three-quarters of an inch 

 from its origin it gives off a branch to the upper lobe of the right lung. This 

 branch is known as eparterial because it is given off above the right pulmonary 

 artery, below which the main bronchus now passes and is known as hyparterial ; 



