964 THE ORGANS OF VOICE AND RESPIRATION. 



the posterior portion, which carries with it the arytenoid cartilages, and thus elongate the vocal 

 cords. 



The Thyro-arytenoidei muscles, consisting of two parts having different attachments and 

 different directions, are rather complicated as regards their action. Their main use is to draw 

 the arytenoid cartilages forward toward the thyroid, and thus shorten and relax the vocal cords. 

 But, owing to the connection of the inner portion .with the vocal cord, this part, if acting sep- 

 arately, is supposed to modify its elasticity and tension, and the outer portion, being inserted 

 into the outer part of the anterior surface of the arytenoid cartilage, may rotate it inward, and 

 thus narrow the rima glottidis by bringing the two cords together. 



The Thyro-epiglottidei may depress the epiglottis ; they assist in compressing the sacculi 

 laryngis. The Aryteno-epiglottideus superior constricts the superior aperture of the larynx, 

 when it is drawn upward, during deglutition. The Aryteno-epiglottideus inferior, together with 

 some fibres of the Thyro-arytenoidei, compress the sacculus laryngis. 



The Mucous Membrane of the Larynx is continuous above with that lining the 

 mouth and pharynx, and it is prolonged through the trachea and bronchi into the 

 lungs. It lines the posterior surface and the anterior part of the upper surface of 

 the epiglottis, to which it is closely adherent, and forms the aryteno-epiglottidean 

 folds which form the laterial boundaries of 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 laryngis. 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. The fore part of the anterior surface and the upper 

 half of the posterior surface of the epiglottis, the upper part of the aryteno- 

 epiglottidean folds, and the true vocal cords are covered by stratified squamous 

 epithelium ; all the rest of the laryngeal mucous membrane is covered by columnar 

 ciliated cells. 



Crlands. 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 free edges of 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 consist of two sets, superior and inferior. The former 

 accompany the superior laryngeal artery and pierce the thyro-hyoid membrane, to 

 terminate in the glands situated near the bifurcation of the common carotid artery. 

 The latter pass through the crico-thyroid membrane, and open into one or two 

 glands lying either in front of that membrane or to the side of the cricoid cartilage. 

 The nerves are derived from the internal and external laryngeal branches of the 

 superior laryngeal nerve, from the inferior or recurrent laryngeal, and from the 

 sympathetic. The internal laryngeal nerve is almost entirely sensory, but some 

 motor filaments are said to be carried by it to the Arytenoideus muscle. It 

 divides into a branch which is distributed to both surfaces of the epiglottis, a 

 second to the aryteno-epiglottidean folds, and a third, the largest, which supplies 

 the mucous membrane over the back of the larynx and communicates with the 

 recurrent laryngeal. The external laryngeal nerve supplies the Crico-thyroid 

 muscle. The recurrent laryngeal passes upward under the lower border of 

 the Inferior constrictor, and enters the larynx between the cricoid and thyroid 

 cartilages. It supplies all the muscles of the larynx except the Crico-thyroid and 

 part of the Arytenoideus. The sensory branches of the laryngeal nerves form 

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

 the mucous membrane. 



