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
we find in the anthropoid apes." (G. Elliot Smith, in
_Descriptive and Illustrated Catalogue of the Physiological
Series of Comparative Anatomy Contained in the Museum of the
Royal College of Surgeons of England_, second edition, vol. ii.)
A full statement of Elliot Smith's investigations, with diagrams,
is given by Bullen, _Journal of Mental Science_, July, 1899. It
may be added that the whole subject of the olfactory centres has