1054 REPORT—1885. 
vertebre, and orbital plate of frontal bone. Ribs, fourteen pairs, the first pair 
double-headed. 
4, Beluga. Killed at Wick, 1884. Skeleton and photograph showing natural 
form, exhibited to the Section. 
2. Is the Commissural Theory of the Corpus Callosum correct ? 
By Professor D. J. Hammron, MB. 
The results recorded by the author were obtained by certain special methods of 
preparation. They went to prove that the corpus callosum is not an interhemi- 
spherical commissure, as is generally supposed, but that it is in reality the decussation 
of a particular system of fibres on their way downwards to join the inner and 
outer capsules. ‘These fibres are not to be confounded with the motor and other 
direct fibres derived from the cerebral cortex which decussate at some point lower 
down. 
The facts bearing upon the above were briefly as follows :—(1) The fibres cax 
be seen with the naked eye turning down to join the two capsules, after issuing at 
each side from the tectorial part of the corpus callosum. 
(2) They can be traced with the microscope from the corpus callosum con- 
tinuously down to the two capsules. 
(38) The mass of fibres thus turning downwards forms an arch, varying in 
shape in different localities, but corresponding in extent to the position of the 
corpus callosum. This arched system of fibres (‘the crossed callosal tract’) can be 
exposed by dissecting off the superjacent cortex and medullary substance, Their 
curved course can then be distinctly seen with the naked eye, 
(4) In young embryos of mammals, and more especially in the human embryo 
of from three to four months, the callosal system of fibres is much more developed 
than any other, and hence it appears to be more differentiated than in the adult, 
where it is obscured by the other systems of fibres around it. The course of the 
fibres in the embryo is exactly similar to that described in the adult. After leaving 
the corpus callosum they curve downwards in a ribbon-like band to join the two 
capsules. 
(5) The brain of a woman fifty-three years of age was shown, in which the 
right first and second frontal convolutions had been destroyed probably in infancy. 
Corresponding with this the tectorial part of the corpus callosum was extremely 
small, and the opposite inner and outer capsules ‘were almost wanting, while those 
on the same side were comparatively well developed. The basal ganglia on the 
opposite side were also extremely small. 
(6) The ultimate destinations of those callosal fibres entering the inner capsule 
are probably the caudate nucleus, the thalamus opticus, the grey matter of the 
pons, the cerebellum (?), the ganglionic masses in the medulla oblongata, and 
possibly the spinal cord. Of those entering the outer capsule the following points 
of attachment had been made out :—the olfactory tract, the optic tract, the inner 
capsule (a few fibres), and the temporo-sphenoidal lobe. 
(7) The callosal fibres derived from the frontal and occipital regions follow 
essentially the same course as those arising from the vertex. 
3. The Evidence of Comparative Anatomy with regard to Localisation of 
Function in the Cortex of the Brain. By Avex. Hin, M.A., M.B., 
M.R.C.S. 
The central nervous system is formed as an inyoluted tube of epiblast, from the 
cells composing which the nerve fibres grow out. Throughout the greater part of 
the system the cells form the inner, the fibres the outer portion of the tube’s wall. 
In its anterior part, where the tube is dilated into the cerebral vesicles, a layer of 
cells is also disposed outside the white fibre tube. Throughout the central grey 
tube the cells are arranged in groups, from which spring the nerve fibres for each 
metamer, the cells in each group being distinguishable into those which are con- 
