The first more highly organized sense to arise on the diffused tactile sensitivity of the skin is, in most cases, without doubt that of smell. At first, indeed, olfactory sensibility is not clearly differentiated from general tactile sensibility; the pit of thickened and ciliated epithelium or the highly mobile antennæ which in many lower animals are sensitive to odorous stimuli are also extremely sensitive to tactile stimuli; this is, for instance, the case with the snail, in whom at the same time olfactive sensibility seems to be spread over the whole body.[24] The sense of smell is gradually specialized, and when taste also begins to develop a kind of chemical sense is constituted. The organ of smell, however, speedily begins to rise in importance as we ascend the zoölogical scale. In the lower vertebrates, when they began to adopt a life on dry land, the sense of smell seems to have been that part of their sensory equipment which proved most useful under the new conditions, and it developed with astonishing rapidity. Edinger finds that in the brain of reptiles the "area olfactoria" is of enormous extent, covering, indeed, the greater part of the cortex, though it may be quite true, as Herrick remarks, that, while smell is preponderant, it is perhaps not correct to attribute an exclusively olfactory tone to the cerebral activities of the _Sauropsida_ or even the _Ichthyopsida_. Among most mammals, however, in any case, smell is certainly the most highly developed of the senses; it gives the first information of remote objects that concern them; it gives the most precise information concerning the near objects that concern them; it is the sense in terms of which most of their mental operations must be conducted and their emotional impulses reach consciousness. Among the apes it has greatly lost importance and in man it has become almost rudimentary, giving place to the supremacy of vision. Prof. G. Elliot Smith, a leading authority on the brain, has well summarized the facts concerning the predominance of the olfactory region in the mammal brain, and his conclusions may be quoted. It should be premised that Elliot Smith divides the brain into rhinencephalon and neopallium. Rhinencephalon designates the regions which are pre-eminently olfactory in function: the olfactory bulb, its peduncle, the tuberculum olfactorium and locus perforatus, the pyriform lobe, the paraterminal body, and the whole hippocampal formation. The neopallium is the dorsal cap of the brain, with frontal, parietal, and occipital areas, comprehending all that part of the brain which is the seat of the higher associative activities, reaching its fullest development in man.