45G THM BE8PIRATOBT AI'rAltATl* l\ \I.\MMALIA. 



inferior border and inner face of the vocal cords. Tho presence of nervous 

 filaments, analogous to those of the trachea, in the sub-glottal part of the 

 larynx may explain the difference, well known to physiologists, that exists 

 between the sensibility of the entrance to tho glottis and that of the inferior 

 border of the vocal cords. 



EXTERNAL SURFACE OP THE LARYNX. It is divided into four planes : a 

 superior, inferior, and two lateral. The superior plane, formed by the ary- 

 teiioid and posterior crico-arytenoid muscles, is covered by the pharynx 

 and oesophagus ; in its anterior moiety, it is directly covered by tho pharyu- 

 geal mucous membrane. 



The inferior plane presents, from before to behind, tho thyro-hyoid 

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

 inferior part of the cricoid cartilage, and the crico-trachcalis ligament. There 

 is remarked, laterally, the inferior border of the thyro-hyoid muscle. Tins 

 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 cartilage, and the alte of tho 

 thyroid. They also show the opening through which passes tho superior 

 laryugeal nerve ; they are related to the crico- and thyro-pharyngeal muscles, 

 as well as the maxillary gland. 



INTERNAL SURFACE OF THE LARYNX. This surface is divided into three 

 perfectly distinct regions : a middle one, named the glottis ; a superior, called 

 the mpraglottic portion ; and an inferior, designated the subglottic portion. 



The glottis (rima glottidii) is a narrow space which affects the figure of a 

 very elongated isoscelated triangle, its base being uppermost. This irregular 

 fissure is comprised between the elastic structures known as the vocal cords. 

 It is the narrowest part of the larynx. 



Tho mpraglottic portion, 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, lateral excavations, 

 dilated at tho bottom, and which penetrate between the anterior border of 

 the vocal cords and the prolongations of the base of the epiglottis, insinuat- 

 ing themselves even between the fasciculi of the thyro-arytenoid muscle 

 (in the Ass and Mule the ventricles are proportionately larger than in tho 

 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 

 arytenoids and the lateral border of the epiglottis, and making a remark- 

 able projection at the bottom of the pharyngeal space. 



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

 directly continuous with the internal canal of the trachea. In front is seen 

 the prominence formed by the posterior border of tho vocal cords : above, 

 a diffused and shallow excavation, placed at tho point of junction of the 

 arytenoid and cricoid cartilages, and which is named tho subarytcnoid sinus. 



FUNCTIONS. As a tube intended for tho passage of a column of air 

 during the act of respiration, tho larynx does not give rise to any very 

 interesting physiological considerations. It is, nevertheless, worthy of remark 

 that this organ, in imitation of tho nostrils, dilates or contracts, according 

 to tho volume of tho column of air introduced into, or expelled from, the 

 lungs, and that its paralysis, during rapid movements, causes an embarrass- 

 ment in tho respiration which betrays itself in " roaring." But a physio- 



