534 RESPIHATOBY APPARATUS IN MAMMALIA. 



The French works on Veterinary Anatomy cite this muscle — we do not know 

 v^rjiy — as a dilator of the larynx. Its position in front of the crico-arytaenoid 

 cartilages sufficiently indicates that it cannot act otherwise than in bringing the 

 two arytgenoid cartilages together. And the continuity of a large number of its 

 fibres with those of the thyro-arytaenoideus, does not allow it to have any other 

 action than that of this muscle. 



3. JIwous membrane of the larynx. — This membrane is only a continuation 

 of that of the pharynx, which, after covering the prominence formed by the 

 opening of the larynx, passes over the circumference of that opening, to be spread 

 on the posterior face of the epiglottis and the internal face of the arytaenoid 

 cartilages, to dip into the ventricles, pass above the vocal cords, line the inner 

 face of the cricoid cartilage, and, finally, to be prolonged into the trachea. Its 

 deep face adheres closely to the parts it covers, except in the lateral ventricles. 

 The free face is perfectly tense, and is covered with stratified tesselated epithelium 

 at the epiglottis and vocal cords, but only with ciliated epithelium elsewhere. 



The superficial layer of its dermis is composed of reticulated tissue except at 

 the vocal cords, where it is closer and has some papillae (Coyne). 



The (jlandulce. of the larynx are racemose ; they are absent on the free border 

 of the vocal cords, but are numerous on the posterior face of the epiglottis, where 

 they are lodged in the minute depressions of the cartilage ; they are also found 

 on the arytaenoid cartilages and the arytaeno-epiglottidean folds. There are 

 closed follicles also in the vestibule of the larynx, at the limit of the arytaeno- 

 epiglottidean folds and the epiglottis, on the posterior surface of the latter. 



The mucous membrane of the larynx possesses an exquisite sensibility, owing to 

 which admission to the air-passage is denied to the solid or liquid alimentary 

 particles, which, during deglutition, might deviate from their normal course and 

 pass into this opening. The slightest touch brings into play this sensibility, 

 and determines an energetic reflex action of the constrictor muscles of the larynx 

 and chest ; from this results the almost complete occlusion of the larynx, and 

 a violent cough which expels the substances that have caused the irritation of the 

 membrane. Every one has experienced the effects of this reflex action, and knows 

 by experience the great sensibility of the larynx. 



4. Vessels and nerves. — Blood is carried into the larynx by the laryngeal 

 ■arteries, which pass between the cricoid and the posterior border of the thyroid 

 cartilages. Their branches spread over the ventricle of the glottis and the thyro- 

 arytaenoid muscle, to be expended in the substance of the muscles and mucous 

 membrane. The terminal ramifications form red plexuses on the surface of cer- 

 tain parts of the larynx. The veins are satellites of the arteries. The lymphatics 

 form a superficial and a submucous network. 



The pru'umoyastric fm-nishes the larynx with its principal nerves — the superior 

 and inferior laryngeal. The first is distributed to the upper part of the organ 

 and the entrance to the glottis, endowing the mucous membrane with that high 

 degree of sensibility which distinguishes it. The second is more especially a 

 motor nerve, and supplies all the muscles, except the crico-thyroid. A filament 

 of the recmTent nerve is distributed in the mucous membrane of the subglottal 

 portion, and to the inferior border and inner surface of the ^•ocal cords. The 

 presence of nerve-filaments, analogous to those of the trachea, in the subglottal 

 part of the larynx may explain the difference, well known to physiologists, that 

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

 border of the vocal cords. 



