"In the early mammals the olfactory areas form by far the greater part of the cerebral hemisphere, which is not surprising when it is recalled that the forebrain is, in the primitive brain, essentially an appendage, so to speak, of the smell apparatus. When the cerebral hemisphere comes to occupy such a dominant position in the brain it is perhaps not unnatural to find that the sense of smell is the most influential and the chief source of information to the animal; or, perhaps, it would be more accurate to say that the olfactory sense, which conveys general information to the animal such as no other sense can bring concerning its prey (whether near or far, hidden or exposed), is much the most serviceable of all the avenues of information to the lowly mammal leading a terrestrial life, and therefore becomes predominant; and its particular domain--the forebrain--becomes the ruling portion of the nervous system. "This early predominance of the sense of smell persists in most mammals (unless an aquatic mode of life interferes and deposes it: compare the _Cetacea, Sirenia_, and _Pinnipedia_, for example) even though a large neopallium develops to receive visual, auditory, tactile, and other impressions pouring into the forebrain. In the _Anthropoidea_ alone of nonaquatic mammals the olfactory regions undergo an absolute (and not only relative, as in the _Carnivora_ and _Ungulata_) dwindling, which is equally shared by the human brain, in common with those of the other _Simiidæ_, the _Cercopithecidæ_, and the _Cebidæ_. But all the parts of the rhinencephalon, which are so distinct in macrosmatic mammals, can also be recognized in the human brain. The small ellipsoidal olfactory bulb is moored, so to speak, on the cribriform plate of the ethmoid bone by the olfactory nerves; so that, as the place of attachment of the olfactory peduncle to the expanding cerebral hemisphere becomes removed (as a result of the forward extension of the hemisphere) progressively farther and farther backward, the peduncle becomes greatly stretched and elongated. And, as this stretching involves the gray matter without lessening the number of nerve-fibres in the olfactory tract, the peduncle becomes practically what it is usually called--i.e., the olfactory 'tract.' The tuberculum olfactorium becomes greatly reduced and at the same time flattened; so that it is not easy to draw a line of demarcation between it and the anterior perforated space. The anterior rhinal fissure, which is present in the early human foetus, vanishes (almost, if not altogether) in the adult. Part of the posterior rhinal fissure is always present in the 'incisura temporalis,' and sometimes, especially in some of the non-European races, the whole of the posterior rhinal fissure is retained in that typical form which