. 
‘Literary Notices. xi 
operculum (thus forming the anterior part of the posterior limb of the 
Sylvian fissure) and also the orbital operculum (which is the anterior 
operculated lip of the fronto-orbital sulcus). The latter meeting gives 
rise to the anterior limb of the Sylvian fissure. It often happens, 
however, that the expanding cortex in the neighborhood of the meet- 
ing place of the anterior and superior limiting sulci becomes accom- 
modated by the formation of an additional operculum—the frontal. As 
the result two anterior limbs of the Sylvian fissure (instead of one) are 
produced. 
It follows from this account that a complete Sylvian fissure exists 
only in the human brain, and that the so-called Sylvian fissure of even 
the Anthropoid Apes lacks properly-constituted anterior limbs, a small 
part of. the posterior limb, and generally also the ‘‘stem” of the com- 
plete sulcus. 
The full development of the opercula leads to the abortion of the 
upper part of the fronto-orbital sulcus in the human brain. 
._ The lateral, post-lateral, and ansate sulci of the Carnivora and 
other Mammalian Orders become in the Primates the intraparietal, 
transverse occipital, and ramus postcentralis superior respectively. It isa 
moot point whether the coronal sulcus, which is so constant and preco- 
cious in the Carnivora, Ungulata, and Edentata, forms the ramus post- 
centralis inferior of the intraparietal system. The evidence seems to 
point to the sulcus rectus and the lower part of the central sulcus as 
being the real derivatives of this furrow. 
In most Apes the region lying behind the transverse occipital sulcus 
undergoes a peculiar modification leading to the formation of a great 
operculum from the posterior lip of a new sulcus, called Simian or, as 
the Germans say, ‘‘Affenspalte.”” This does not usually occur in the 
human brain, probably because the cortical areas around the transverse 
occipital sulcus undergo a greater expansion than is the case in the 
Apes. 
I have seen, however, in the brain of an Egyptian fellah a small 
indubitable Simian sulcus like that of the Gorilla. It was separated by 
a considerable interval from the mesial plane. 
It thus happens that this region of the human brain more closely 
resembles the condition found in many of the larger Cebidz (in which . 
the opercular formation has either not begun or is only just commenc- 
ing) than that of the Anthropoid Apes. Of the latter the brain of the 
Gorilla approaches the human condition much more nearly than does 
that either of the Chimpanzee or Orang. It must be remembered, 
however, that the ‘‘occipital” and ‘‘insular” regions exhibit an extra- 
ordinary amount of variation in each of the Simiide ; the average con- 
dition of these two changing areas is much nearer the human type in 
the Gorilla than in either of the other great Apes. 
Of the other sulci of the human brain (besides those already 
discussed) the only ones which can be called ‘‘old” in the phylogenetic 
sense are the orbital and possibly the inferior frontal sulci. 
The orbital sulcus is probably one of the most primitive furrows 
in the neopallium, if not the earliest. It is the only sulcus found in the 
