Page:The New International Encyclopædia 1st ed. v. 14.djvu/757

NOSE. 645 NOSE. tion of nucleated particles, of nearly uniform appearance throughout, except that the lowest ones are of a darker color than the rest, from their containing a brown pigment in their in- terior. The olfactory region ahounds in glands, apparently identical with sweat glands, which dip down in the recesses of the submucous tissue among the ramifications of the olfactory nerve. They are named Bowman's glands. The nerves of the nose are the first i)air or olfactory, which are s])ecially connected with the sense of snudl; branches of the fifth pair, whieh confer ordinary sensibility on its skin and nuicous membrane: and motor filanientt?, from the facial nerves to the nasal muscles. The olfactory nerve on each side is connected with the inferior sur- face of the brain by an external, a middle, and an internal root, which unite and form a flat band (or, more correctly, a prism), which, on reaching the cribriform plate of the ethmoid bone, expands into an oblong mass of grayish- white substance, the olfa<'tory bulb. From the lower surface of this bulb are given off the olfaetor}- filaments, fifteen or twenty in ninnber, which pass through the cribriform foramina, and are distributed to the mucous membrane of the olfactory region. The branches of the fifth pair (or trifacial) given to the nose are the nasal nerve (derived from the ophthalmic division), which supplies the skin and mucous membrane in the vicinity of the nostrils, and the naso- palatine nerve (derived from Meckel's ganglion, which is connected with the superior maxillary division), which supplies the nuicous membrane on the spongy bones and on the septum. What- ever may be the nature of the odorous matter, it is necessary- that it should be transmitted by a respiratory current through the nostrils to the true olfactory region, and dissolved or suspended in the fluid with which the olfactory membrane is normally covered. The ])roper condition of this fluid is one of the essential conditions of the perception of odors. If the membrane is too dry. or if there is an inordinate excretion of fluid from its surface (both of which conditions occur in catarrh or cold in the head), smell is impaired or lost, in consequence of the necessary penetration of the stimulating odor to the nervous filaments being prevented. It has been observed that when the nostrils are filled with rose water or eau de Cologne, no odor is perceived, and simply filling the nostrils with distilled water suspends for a time the sense of smell. If, on the other hand, the scent lie dissolved in 'normal saline solution,' which closely resembles the natural secretion, the odor is perceived. ■The sense of taste is often confused with that of smell, ^^'e speak of 'tasting' an odoriferous substance, such as an onion, or ii savory dish, or a wine, when in reality we perceive it through the olfactory nenes. This is proved by the fact that the taste for these substances is lost when the smell becomes impaired. The acuteness of the sense of smell is far greater in many of the lower animals (dogs, for e.xamplc) than in man. and they employ it in guiding them to their food, in warning them of approaching danger, and iov other purposes. To civilized men the utility of this sen.se is compara- tively small; but it is occasionally much in- creased when other senses are deficient. Among many savage tribes the sense is almost as acute as in many of the lower mammals. See Nos- trils; Smell. NOSE, Comparative Anatomy of the. In the ordinary usage of the word, no animals but mamnuils have noses; but in the widest sense of an organ of smell, the nose is foiuid in all vertebrates and in some lower animals. Owing to the close relation that e.xists i)et«cen the sen.se of taste and the sense of snudl, it is impossible to determine beyond question the func- tion of certain organs among the lower animals, but in several cases evi<lence has been produced to sliow that ciliated pits or patches have a function similar to, if not identical with, that of smell in vertebrates. Thus as low as the ctenophores and some medusa', there occur special areas covered with cilia, to which the sense of taste or smell has been assigned. In many Hat- worms, in nemerteans, and in many true worms, ciliated grooves, ])its, and prominences occur, which are certainlj' sensory and probably olfac- tory. Whether organs of smell occur among crustaceans and insects is not beyond doubt, but short processes, open at the point and uitli special nerve connections located on the an- tenna', are regarded as organs of smell. There is much evidence in suiii)ort of the belief that insects smell, and the antenna- are almost cer- tainly the seat of whatever such sense they possess. Among echinoderms there are isolated cases of organs which may be olfactory, notably the sensory cups on the inner surface of the tentacles in Synapta. Among the moUusks, the patches of densely ciliated epithelium in the mantle-cavity, known as 'osphradia.' are very probably organs of smell. In Amphioxus and the cjclostomes there is a single pit or sac, lined with an epithelium consisting of ciliated and sensory (olfactory) cells. In the elasinobranch fishes the olfactory sacs lie on the under surface of the snout, but in all the vertebrates they are situateil somewhere between the eyes and the end of the snout, on the upper surface. In all animals aliove cyclostomes the nasal sacs are inclosed in cartilaginous or bony cases, forming a prominent part of the skull. The nostrils of bony fishes are divided into two parts by a septum, which is .sometimes so wide as to give rise to four wholly distinct nostrils. The mucous membrane lining the nasal sacs of fishes is raised up into a number of complex radial folds, thus increasing the sensory surface. The dipnoid fishes differ from the other true fishes in that the nasal sacs communicate with the cavity of the month as well as with the exterior, just as they do in all iiigher vertebrates. In amphi- bians we find for the fir.st time turbinal bones which serve to increase the sensory surface of the nasal cavities. There are also glands present in the sensory epithelium, serving to keep it moist. Moreover, there is a canal connecting the anterior angle of the orbit with the nasal cavity, known as the naso-lachrymal duct, which is of use in conveying surplus lachrymal secretion (tears) into the nasal cavity and flicnce into the pharynx through the posterior nares. This duct is present in all the higher vertebrates also. In re|itilcs the olfactory organ is rather simple, especially in lizards and snakes; there is only a single turbinal, though crocodiles have on the outer side of the cavity a second prominence called the pseudo-turbinal. Birds also have only