TRANSACTIONS OF SECTION D. 1055 
nected with sensory, those which are connected with motor, and those which are 
connected. with visceral fibres. The central grey tube includes the optic thalamus, 
and the key to its constitution is to be found in its segmentation. 
The object of this investigation is to determine the relation borne by the 
several parts of the peripheral grey tube (the cortex mantle) to the segments of 
the central grey tube, and indirectly, therefore, to the several body nerves. It may 
be that the processes of the cells of the central grey tube, the commissural nerves, as 
they may be called, are woven, as it were, when they reach the cortex into a colour- 
less web, or, on the other hand, they may retain and impart to separate regions of the 
cortex the tone which they have received from sense organ and motor mechanism. 
The latter of these suppositions is supported by experimental research, for stimula- 
tion of particular regions of the cortex indicates the occupation of those regions 
by the cerebral centres of particular nerves. On such evidence is based the theory 
of ‘localisation of function.’ Eventually, however, this theory must be sub- 
mitted to a comparative test. Animals differ from one another widely in their 
sensory and motor endowments. Such differences are clearly indicated by the 
varying cross-sections of their several nerves, and if particular regions of the cortex 
are in functional relation with particular nerves, the extent of their development 
will vary with the size of the nerves. To the superticial regional development of 
the cortex the fissures are the only possible guides. It is, therefore, of the hichest 
importance to determine their homological value ; that they may he safely accepted 
as boundary-lines is shown by the constancy of their arrangement in animals of any 
one type, the uniformity of their development and progressive extension, and the fact 
that the first to appear are the most constant in the animal series and the deepest in 
the individual. ‘To reduce the matter to statistics, the superficial areas of regions 
bounded by certain fissures should be compared with the cross-sections of their 
correlated nerves. As yet no system of mensuration has been devised for the 
cortex. In the more divergent animals, however, the proportional development of 
the various regions of the cerebrum is obvious to the eye. 
In herbivora, which depend for safety upon sight and upon repeated simple 
movements of the limbs, the internal part of the occipital lobe, as shown by the 
deflection of the lateral fissure, is large, the sigmoid gyrus small. In carnivora, 
which depend for their food upon the sense of smell and the complexity of their 
muscular system, the temporo-sphenoidal lobe and the sigmoid gyrus are both con- 
spicuous for their development. That these great differences do not depend upon 
the distance apart of the animals phylogenetically is shown by the fact that in the 
pig, which seeks its food with its nose, the brain approaches the carnivorous rather 
than the herbivorous type. Amongst carnivora the otter is conspicuous for the 
small deyelopment of its olfactory apparatus; the temporo-sphenoidal lobe is cor- 
respondingly small. In this animal the fifth nerve is very large, which accounts 
apparently for the large size of the convolution which lies in front of the fissure of 
Sylvius. Cats are remarkable tor the uniform development of their senses. With 
this uniformity is associated a remarkable symmetry of brain. Hearing, however, 
is in these animals particularly acute ; the cortical localisation of this sense appears 
to be above the processus acuminis of the fissure of Sylvius. In the main these results 
are confirmatory of those obtained by Ferrier and other experimental physiologists. 
The order in which the centres are situate on the cortex indicates that the cerebrum 
has undergone a rotation backwards into a single turn of a spiral coil. 
4. Report of the Committee for the Exploration of Kilima-njaro and the 
adjoining Mountains of Hastern Equatorial Africa.—See Reports, p. 681. 
5. Report of the Committee for arranging for the occupation of a Table at 
the Zoological Station at Naples.—See Reports, p. 466. 
