Literary Notices. xiii 
ramus  post-centralis superior is almost as __ sure. We 
find in the carnivora and the Primates respectively a 
deep and important sulcus bearing the same relations to the ansate and 
lateral sulci. In the former we call it ‘‘crucial’” and in the latter 
‘central’; the solution thus naturally suggested is that the central sulcus 
of.the Primates represents the crucial sulcus of the Carnivora. Such a 
view has often been propounded before, and has in several instances 
been disregarded for no valid reason. Thus it has been urged (with a 
singular disregard for the facts of the case) that the crucial sulcus ‘‘be- 
longs to the mesial wall,” in spite of the patent evidence afforded by 
the Arctoid Carnivora that when the crucial sulcus becomes dissociated 
from the intercalary sulcus it often lies wholly on the dorsal surface of 
hemisphere (see the brain of the Bears, the Glutton, and in fact most 
of the Arctoidea). 
If we study the forms assumed by the crucial sulcus in the large 
Carnivores (such as the Bears and Seals) and by the central sulcus in 
the large Apes (Simiidz), we cannot fail to be struck with a striking 
parallelism, which could only be produced by the operation of similar 
factors in the two cases. Moreover, the earliest phases of the develop- 
ment of the central sulcus in the Lemurs are similar to the first rudi- 
ments of the crucial sulcus in the Viverride. 
Physiological evidence (which, however, in such matters is notor- 
iously misleading) does not altogether support such an homology. In 
the Anthropoidea the central sulcus sharply marks the exact caudal limit 
of the area of excitable cortex, whereas in the Carnivora (so the physiolo- 
gists tell us) the crucial sulcus lies in the midst of the excitable area. 
If we admit the homology of the central and crucial sulci we shall 
(by comparison with the behaviour of the latter) find an explanation of 
many features of the former. According to such an hypothesis a glance 
ata Bear’s brain will at once make intelligible the meaning of the super- 
ior genu, the caudal bend in the mesial extremity, and the tendency of 
the central sulcus in the Anthropoid Apes and Man to extend on to 
the mesial surface in front of the upturned end of the calloso-mar- 
ginal sulcus. 
In the features of its central sulcus (the relative positions of the 
genua and the behaviour of the mesial extremity of the sulcus) the 
Anthropopithect approach much nearer to Man than does the Orang or 
any other Ape.’ 
The human brain is distinguished from those of the Apes by the 
abundance of sulci between these stable and constant elements. 
The superior frontal and especially the middle frontal sulci are 
much better developed than in the Apes, and innumerable sulci develop 
in connection with these. The inferior transverse sulcus (so constant 
1 As the result of further investigations since the above was written, I 
have come to the conclusion that the crucial sulcus represents the dorsal part 
of the central sulcus and that the ventral part of the latter is formed either 
from or at the expense of (mechanically) the caudal extremity of the coronal 
sulcus. 
' 
