THE TRACHEA 523 



ordinary breathing the rima is somewhat lanceolate in form (Fig. 465) ; when dilated, 

 it is diamond-shaped, the widest part being between the vocal processes. The 

 narrow part of the glottis between the vocal cords is termed the glottis vocalis (Pars 

 intermembranacea), while the wider part between the arytenoid cartilages is the 

 glottis respiratoria (Pars intercartilaginea). 



In the revised nomenclature the terms "true" and "false" vocal cords have been replaced 

 by "labium vocale" and " phca ventrioularis. " The labium vocale consists of the plica vocalis, 

 hg. vocale, and m. vocalis; the last forms the bulk of the projection. 



The posterior compartment of the laryngeal cavity is directly continuous with 

 the trachea. It is enclosed by the cricoid cartilage and the crico-thyroid membrane. 

 It is clearly marked off laterally by the vocal cord and the projection caused by the 

 posterior border of the arytenoid cartilage. It is oval in form, the transverse 

 diameter being an inch and a half to two inches (ca. 4 to 5 cm.), and the dorso- 

 ventral diameter two to two and a half inches (ca. 5 to 6 cm.). 



The mucous membrane of the larynx (Tunica mucosa laryngis) is reflected 

 around the margin of the aditus to become continuous with that of the pharynx, 

 and is continuous behind with that which hues the trachea. It is closely attached 

 to the epiglottis, except at the base, but elsewhere in the aditus and vestibule it is 

 loosely attached by submucous tissue which contains many elastic fibers. It is 

 thin and very closely adherent over the vocal cords and the medial surfaces of the 

 arytenoid cartilages. The epithelium is of the stratified squamous type from the 

 aditus to the glottis, beyond which it is columnar ciliated in character. There are 

 numerous mucous laryngeal glands (Glandulaj laryngesB), except in the glottis and 

 the pharyngeal surface of the epiglottis, in which situations they are scanty. Ljnmph 

 nodules (NoduU lymphatici laryngei) are also present, especially at the lateral 

 ventricle. 



Vessels and Nerves. — The arteries are derived from the laryngeal and ascend- 

 ing pharyngeal arteries. The veins correspond to the arteries. The lymph- 

 vessels go to the anterior cervical and pharyngeal lymph glands. The nerves 

 come from the vagus. The recurrent or posterior laryngeal is the motor nerve to 

 the muscles with the exception of the c rico-thyroideus. The anterior laryngeal 

 is the sensory nerve; it commonly supplies the nerve to the crico-thyroideus. 



THE TRACHEA 



The trachea extends from the larynx to the roots of the lungs, where it divides 

 into the right and left bronchi. It is kept permanently open by a series of fifty to 

 sixty incomplete cartilaginous rings embedded in its wall. It occupies a median 

 position, except near its termination, where it is pushed a little to the right by the 

 arch of the aorta. It is approximately cylindrical, but its cervical part is for the 

 most part depressed dorso-ventrally by contact with the longus colli muscle, so 

 that the dorsal surface is flattened. Its average length is about 30 to 32 inches (ca. 

 75 to 80 cm.). The average caliber is about two to two and one-half inches (ca. 5 to 

 6 cm.), but in the greater part of the neck the transverse diameter is greater and the 

 dorso-ventral smaller.^ It is enclosed by a fascia propria. 



In its cervical part (Pars cervicalis) the trachea is related dorsally to the 

 oesophagus for a short distance, but chiefly to the longus colli muscles. It is related 

 laterally to the lateral lobes of the thyroid gland, the carotid artery, the jugular 

 vein, the vagus, sjonpathetic, and recurrent laryngeal nerves, and the tracheal 



^ At its origin the trachea is almost circular in cross-section and the average diameter is 

 about two and a quarter inches (ca. 5.5 cm.). It soon becomes flattened dorso-ventrally, so that 

 the transverse diameter may be nearly three inches (ca. 7 cm.) and the dorso-ventral about two 

 inches (ca. 5 cm.). In the thorax the diameters become more nearly equal, and sometimes the 

 -dorso-ventral diameter is the greater; this is the case where the aorta crosses the trachea. 



