80 Roaring in Horses. 



cartilage to the process! musculares of the arytsenoid carti- 

 lages, and when they contract they rotate these downward 

 and inward, bringing the process! vocales of these cartilages 

 nearer each other, and so carrying the vocal cords into appo- 

 sition, closing the space designated the fars vocales (Fig. 5, 

 C). In this they are assisted by the other two pairs of 

 muscles, which, however, are more concerned perhaps in 

 the production of the voice, by shortening and elongating 

 the vocal cords. As the study of the voice has no place in 

 the subject we are now discussing, further description of 

 these muscles is unnecessary. 



Ligaments. — We have already referred to these. 



Mucous Membrane. — The larynx is lined by mucous 

 membrane, which is continuous with that of the mouth and 

 its wide termination, the pharynx. The same membrane also 

 lines the trachea and bronchial tubes, and in the larynx itself 

 forms on each side the pouch or sac known as the " vocal 

 ventricle sac," " lateral sinus " (sacoulus laryngis, sinus 

 lateralis), or " Morgagni's ventricle " ; it likewise constitutes 

 a smaller cavity at the base of the epiglottis, above the 

 origin of the vocal cord at the thyroid cartilage called the 

 "middle sinus " or " sac " {sacculus laryngealis), or " sub- 

 epiglottic sinus." Another sinus — the " sub-aryta?noid " — is 

 found at the crico-arytsenoid joints. It is covered with 

 squamous epithelium at its upper part, below this by 

 ciliated epithelium, and is abundantly supplied with mucus- 

 secreting (muciparous) glands, which are most abundant 

 in the vocal ventricles, the ary-epiglottic folds, and the 

 epiglottis, but none are found in the mucous membrane 

 covering the vocal cords. The membrane varies in thick- 

 ness in different parts of the laryngeal cavity, and the 

 sub-mucous connective tissue is also variable in quantity, 

 being abundant in some situations and very scanty in 

 others. For instance, the membrane is thinnest and has 

 least connective tissue, and is, consequently, most adherent, 

 on the vocal cords and lower part of the arytsenoid carti- 



