NOSE, COMPARATIVE ANA IOMY OF TIIE. In the ordinary usage of the word, no animals but mammals have noses; hut in the widest sense of au organ of smell, the nose is found in all vertebrates and in some lower animals. Owing to the close relation that exists bet \Num the sense of taste and the sense of smell. it is impossible to determine beyond question the func tion of certain organs among the lower animals, lint in several cases evidence has been produced to show 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 aml sonic meduse, there occur special areas covered with cilia, to which the sense of taste or smell has been assigned. In ninny flat worms, in nemorteaus, and in many true worms, eiliated grooves, pits. and prominences occur, which are certainly sensory and probably olfac tory. Whether organs of smell occur among crustaceans and insects is not beyond doubt, lint short processes, open at the point and with special nerve connections located on the an tenna, are regarded as organs of smell. There is much evidence in support of the belief that insects smell, and the antennae are almost cer tainly the seat of whatever such sense they possess. Among echinoderms there are isolated cases of organs which may lie olfactory, notably sensory cups on the inner surface of the tentacles in Synapta. Among the mollusks, the patches of densely ciliated epithelium in the mantle-cavity, known as 'osphradia.' are very probably organs of smell. In Amphioxus and the cyclostomes there is a single pit or sae, lined with an epithelium consisting of eihated and sensory (olfactory) cells. in the elasmobranch fishes the olfactory sacs lie on the under surface of the snout, but in all the vertebrates they are situated somewhere between the eyes and the end of the snout, on the upper surface.
In all animals above cyclostomes the nasal saes are inclosed in cartilaginous or bony eases, 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 diimoid fishes differ from the other true fishes in that the nasal sacs communieate with the cavity of the mouth as well as with the exterior, just as they do in all higher vertebrates. In amphi bians we find for the first 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. Mon.over, t1n.re is a canal connecting the anterior angle of the orbit with the nasal cavity, known as the naso-laehrymal duct, which is of use in conveying surplus lachrymal secretion (tears) into the nasal cavity and thence into the pharynx through the posterior mires. This duet is present in all the higher vertebrates also. In reptiles the olfactory organ is rather simple, especially in lizards and snakes; there is only a single turldnal. though crocodiles have on the outer side of the cavity a second prominence culled the pseudo-turbinal. Birds also have only single true turbinal, hut two are present, and the title 1.11thitIDI is often more ur It'S rolled on In mammals the nasal cavity is large, and the turbinals are extended to form a spongy labyrinth. the projections of which, known as olfactory scrolls, are normally live in number. though they sometimes become more or less fused in pairs. Thus there is sometimes one, but usually two, superior or upper turbinals, and there is usually ono, but sometimes two, middle turbinals. The superior and middle turbinal, of man are somewhat different in their origin. but the inferior turbinal is derived from and corresponds to the single binal of reptiles and birds.