883. The MEATUSES are passages that extend backward, from the nostrils, into which are several openings. They are lined by a mucous membrane, called the _pi-tu´i-ta-ry_, or _schneiderian_, from Schneider, who first showed that the secretion of the nasal fossæ proceeded from the mucous membrane, and not from the brain. -=-=-=-=-=-=-=-=-=-=-=-= 882. What terms are applied to the spaces between these processes? What does fig. 135 represent? 883. Define the meatuses. By what are they lined? -=-=-=-=-=-=-=-=-=-=-=-= 884. Upon the mucous membrane of the nasal passages, the olfactory nerve ramifies, and also a branch of the fifth pair of nerves. This membrane is of considerable extent in man; and in those animals whose sense of smell is very acute, it is still more extensive. [Illustration: Fig. 136. A side view of the passage of the nostrils, and the distribution of the olfactory nerve. 4, The olfactory nerve. 5, The fine and curious divisions of this nerve on the membrane of the nose. 6, A branch of the fifth pair of nerves.] PHYSIOLOGY OF THE ORGANS OF SMELL. 885. The sense of smell enables us to discern the odor or scent of any thing. When substances are presented to the nose, the air that is passing through the nostrils brings the odoriferous particles of matter in contact with the filaments of the olfactory nerves, that are spread upon the membrane that lines the air-passages, and the impression is then transmitted to the brain. -=-=-=-=-=-=-=-=-=-=-=-= 884. What nerves ramify upon this membrane? What is represented by fig. 136? 885-899. _Give the physiology of the organs of smell._ 885. How does the mind become sensible of odoriferous particles? -=-=-=-=-=-=-=-=-=-=-=-= 886. This sense, with that of taste, aids man as well as the inferior animals, in selecting proper food, and it also gives us pleasure by the inhalation of agreeable odors. The sense of smell, like that of taste and touch, may be improved by cultivation. It likewise varies in different persons. _Observation._ Sometimes this sense seems to possess a morbid degree of acuteness in respect to odors, which is highly inconvenient and even dangerous. With some individuals, the smell of certain fruits, flowers, cheese, &c., produce nausea and even convulsions. 887. In the inferior animals generally, the sense of smell is more acute than in man. Thus the bloodhound will track the hare over the ground for miles, guided only by the odor that it leaves in its flight. He also traces the progress of his master through thickly-crowded streets, distinguishing his footsteps from those of a thousand others, and amidst the odorous particles emanating from a thousand sources.