STRUCTURE OF THE BRAIN IN RODENTS. 
741 
4. The cortex of the olfactory bulb and lobe is represented in the olfactory area of 
the nucleus caudatus. 
5. The cortex of the inferior limbic lobe will also be strongly represented in the 
extension of the lenticular nucleus in this direction. 
The callosal commissure. — According to the researches of Fovtlle the fibres of the 
corpus callosum are distributed to none of the convolutions of the brain, but consist 
of tegmental fibres which, having passed upwards through the thalamus and corpus 
striatum, unite over these ganglia as a true commissure of the crus cerebri. All my 
fresh preparations lead me to regard this conclusion as quite fallacious, and demon¬ 
strate in the dearest possible manner the passage of the callosal fibres from the 
convolutions of one hemisphere to those of the other. As maintained by Arnold, 
Oellacher, and Meynert, it is truly and exclusively a commissure of the hemispheres. 
In vertical sections of the brain the following facts I have repeatedly and satisfactorily 
demonstrated. In sections thus taken through the region of the septum lucidem, the 
callosal commissure upon entering either hemisphere meets the mass of- the projection 
system obliquely, and decussating and interweaving with this system proceeds along 
the curved centric pole of the striate body, becoming more and more attenuated as it 
extends along the lateral aspects of the ganglia, owing to the constant distribution of 
fibres from its mass to the cortex throughout the whole of this course. In the first 
part of its course, where it first blends with the projection fibres to the ganglia, a very 
large proportion of its mass (one-third to one-eighth of the whole) takes a curved 
course upwards and inwards so as to reach the median and marginal cortex here 
(Plate 49, fig. 12, 6). By far the greater part accompanies the projection fibres, being 
similarly distributed, viz.: to the cortex of the upper marginal border of the hemi¬ 
sphere and the region just external to it. At this curve of the corpus callosum, 
where it interweaves with the projection fasciculi prior to their dispersion as coronal 
radiations, an angular projection is formed which, taking the whole length of the 
commissure into consideration, really is a prolonged ridge astride which rests the 
longitudinal fasciculus of the olfactory arcuate system (Plate 49, fig. 12, 7 ). In 
vertical sections taken through more posterior planes, it is seen that the portion of the 
callosal commissure which thus supplies the inner marginal regions of the hemisphere 
is distinctly to be traced through the whole of its extent as separate from the lower 
segment which supplies the cortex further outwards. So notably is this the case that 
all prepared sections show, as a rule, a distinct separation between these two callosal 
segments* the inner as it were peeling away from the outer—a natural condition due 
to their opposed direction. It is therefore obvious, at a first glance, that these inner 
regions of the brain which are similar and identical are connected by the same series 
of fibres, and the same may readily be maintained for the outer regions of the hemi¬ 
spheres. In fact, the regular superposition of fibres above one another, and the great 
uniformity of their course in either hemisphere, conclusively show that they unite 
identical regions of both sides. The most inferior fibres of the callosal commissure are 
