vi JouRNAL OF COMPARATIVE NEUROLOGY. 
(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 Simiide, the Cercopithecidz, and the Cebide. But all the 
parts of the rhinencephalon, which are so distinct in macrosmatic mam- 
mals, can also be recognised 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 attach- 
ment of the olfactory peduncle to the expanding cerebral hemisphere 
becomes removed (as a result of the forward extension of the hemi- 
sphere) progressively farther and farther backward, the peduncle be- 
comes greatly stretched and elongated. And as this stretching involves 
the grey matter without lessening the number of nerve-fibers in the 
olfactory tract, the peduncle becomes practically what it is usually 
called, z. 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 tempor- 
alis,”’ and sometimes (D. 710), especially in some of the non-European 
races, the whole of the posterior rhinal fissure is retained in that typi- 
cal form which we find in the Anthropoid Apes. When this occurs we 
can easily recognise the caudal limits of the pyriform lobe, which other- 
wise becomes confused with the neopallium. 
The hippocampal fissure is of a peculiarly consistent nature, and is 
found in all mammalian brains from Orasthorhynchus to Homo. The 
rhinal fissure is equally sus generis and almost as constant as the hippo- 
campal. <A few small mammals, such as Voforyctes, Chlamydophorus, 
Chrysochloris, and some small Chiroptera, have no rhinal fissure. 
Of the sulci perhaps the most constant is. the calcarine, which is 
found in the Marsupials (both Poly- and Diprotodont), in the larger 
Chiroptera, Galeopithecus (but not in any true Insectivore, nor, strange 
to relate, Rodent, so far as I am aware), and in all the Edentates, Car- 
nivores, Ungulates, Cetaceans, and Primates. ‘This wide distribution 
of the calcarine sulcus is not generally admitted, for most writers re- 
gard the calcar avis and the calcarine sulcus as the special prerogative 
of the Primates or even Anthropoidea, and in the celebrated contro- 
versy of 1864 the late Professor Owen strove to prove that it was con- 
fined to the human brain. It is, however, the most primitive (it may, 
however, first appear at the same time as the orbital and suprasylvian 
sulci) and widely prevalent neopallial sulcus in the Mammalia. It 
makes its appearance in most mammals (soon after the hippocampal 
and rhinal fissures have developed) as a short oblique sulcus behind 
the splenium of the corpus callosum (or in the corresponding situation 
in Marsupials), and hence it is commonly called ‘‘ splenial” (Krueg) in 
non-Primate Orders, in which its true nature has not been properly 
recognised hitherto. * 
1 Meynert and Ziehen have called the splenial sulcus ‘‘calcarine” in some 
Carnivores, without indicating any valid reasons for their views. They have 
