The =olfactory mucosa=, or that part to which the olfactory nerve is distributed, and which therefore acts as the sensory surface, is confined to the dorsocaudal parts of the nasal cavity, in the region occupied by the cells of the ethmoid. The air penetrates to this region probably only by a definite act of snuffing, the inferior meatus serving as the usual passageway of air to the lungs. The =nasopharynx= and =pharynx= are considered under the alimentary canal (page 231). 2. =The Larynx.= The larynx is the enlarged upper end of the air-passage which leads from the pharynx to the lungs. It is a box composed of pieces of cartilage connected by ligaments and moved by muscles, and it is lined by mucous membrane. At the root of the tongue about one centimeter caudad of the body of the hyoid bone is the triangular leaf-like =epiglottis= (Fig. 95, _e_, page 227). When food is taken this closes the opening into the larynx, and the food passes over it into the œsophagus. It is so curved that its apex is directed craniad. A fold of mucous membrane, the =plica glossoepiglottica= or =frenulum= of the epiglottis, extends from the middle of its cranial surface to the root of the tongue, and on each side of this fold is a depression. From each side of the base of the epiglottis a fold, =plica aryepiglottica= (Fig. 95, _f_), extends caudad to the base of the arytenoid cartilage (_g_). Dorsad of this fold and separated from it by a depression is a ridge which marks the position of the caudal hyoid cornu. The plicæ aryepiglotticæ (_f_) and the epiglottis (_e_) form the boundaries of the =aditus laryngis=, or opening into the larynx. The cavity of the larynx is divided into three portions. The upper one of these is the =vestibule= of the larynx. It is bounded caudad by two folds of mucosa (_i_) that stretch from the caudal surface of the epiglottis near its base to the tips of the arytenoid cartilages. These folds are the =false vocal cords= (_i_). Their vibration is said to produce purring. Caudad of the false vocal cords two folds of the mucosa stretch from the apices of the arytenoid cartilages to the thyroid cartilages, near the base of the epiglottis. These folds are nearer the median plane than the false vocal cords. They are the =true vocal cords= (_j_). The =middle portion= of the laryngeal cavity is that between the true and the false vocal cords. It is produced laterally into a very small pouch or pocket on each side, the =ventriculus=. The narrow slit between the true vocal cords is the =glottis= (_h_). It can be narrowed and widened by the action of muscles. The vocal cords, which bound it, are set vibrating by currents of air transmitted from the lungs, and the voice-sounds are thus produced. The =caudal portion= (inferior portion) of the laryngeal cavity is that between the glottis and the first tracheal cartilage. It is narrowed near the glottis.