THE LARYNX. 



535 



Fig. 316 



External Surface of the Larynx. — It is divided into four planes : a 

 superior, inferior, and two lateral. The superior 'plane, formed by the arytaenoid 

 and posterior crico-arytasnoid muscles, is covered by the pharynx and oesophagus ; 

 in its anterior moiety, it is directly covered by the pharyngeal mucous membrane. 



The inferior plane presents, from before to behiud, the thyro-hyoid mem- 

 brane, the body of the thyroid cartilage, the crico-thyroid membrane, the inferior 

 part of the cricoid cartilage, and the crico-trachealis ligament. There is remarked, 

 laterally, the inferior border of the thyro-hyoid muscle. This plane corresponds 

 to the scapulo-hyoideal muscles, which entirely cover it. 



The lateral planes exhibit the external faces of the thyro-hyoid and crico- 

 thyroid muscles, that of the cricoid cartUage, and the alae of the thyroid. They 

 also show the opening through which passes the superior laryngeal nerve ; they are 

 related to the crico- and thyro-pharyngeal muscles, as well as the maxillary gland. 



Internal Surface of the Larynx (Fig. 316). — This surface (or cavum 

 laryngis) is divided into three perfectly distiuct regions : a middle, named the 

 glottis; a s,ni^TioT,ca\]ed the supra-glottic portion ; and 

 an inferior, designated the infra- or sub-glottic flortion. 



The glottis {rima glottic/is) is a naiTOw space in 

 the form of a very elongated isoscelated triangle, its 

 base being uppermost. This irregular fissure is com- 

 prised between the elastic structures known as the 

 vocal cords. It is the narrowest part of the larynx. 



(The space between the vocal cords is designated 

 the glottis vocalis, pars vocalis, or interligamentous 

 portion ; that between the arytgenoid cartilages, the 

 glottis respiratoria, ^mrs respiratoria, or intercartila- 

 ginous portion.) 



The supra-glottic portion {aditus ad laryngem, 

 introitus laryngis), wider than the glottis, but always 

 greatly depressed on each side, particularly in the 

 region comprised between the arytenoids, presents : 

 1. The two ventricles of the larynx {Morgagni's ven- 

 tricles), lateral excavations, dilated at the bottom, 

 which penetrate between the anterior border of the 

 vocal cords and the prolongations of the base of the 

 epiglottis, insinuating themselves even between the 

 fasciculi of the thyro-aryttenoid muscle (in the Ass 

 and Mule the ventricles are proportionately larger than in the Horse, and open 

 close to the base of the epiglottis). 2. The subepiglottic sinus, a deep depression 

 at the base of the epiglottis, which is provided, in the Ass and Mule, with a thin 

 membrane, capable of vibrating. 3. The entrance of the larynx, or pharyngeal 

 opening of the cavity, a vast, gaping aperture of an oval form, circumscribed by 

 the anterior border of the arytaenoids and the lateral border of the epiglottis, and 

 making a remarkable projection at the bottom of the pharyngeal space. 



The subglottic portion of the larynx is the widest of the three ; it is directly 

 continuous with the canal of the trachea. In front is seen the prominence 

 formed by the posterior border of the vocal cords : above, a diffused and shallow 

 excavation, placed at the point of junction of the arytgenoid and cricoid car- 

 tilages, named the subarytcBuoid sinus. 



Functions. — A« a tube intended for the passage of a column of air during 



ENTRANCE TO THE LARYNX 

 OF THE HORSE. 



i, Glottis ; B, epiglottis ; c, 

 entrance to the lateral ven- 

 tricle ; D, vocal cord ; E, 

 oesophageal infun^iibulum 

 opened ; f, f. posterior pil- 

 lars of the soft palate. 



