402 Proceedings of the Royal Society of Edinburgh. [Sess. 
other paths than the pyramidal tract, an alternative path being furnished 
by the ventral columns and ventral parts of the lateral columns of the cord. 
3. Methods. 
The cerebral hemispheres of the guinea-pig were first hardened in 
graduated baths of alcohol, then cleared with cedar oil and embedded in 
paraffin. Sections were then made 10 ^ in thickness and stained by 
Nissel’s method. 
One hemisphere was cut in a complete series of transverse sections, 
from the posterior to the anterior pole, great care was taken to preserve 
the full sequence of these sections. From this series a general idea was 
got of the lamination of the cerebrum, and the extent and distribution of 
the various types of cortex. It was, however, impossible to make any 
estimations of the depth of the cortex, owing to the obliquity which is 
unavoidable in a continuous series of sections through a cerebral hemisphere. 
A second hemisphere was therefore mapped out into suitably sized blocks, 
cut and stained. The position, size, shape, and relationship of these blocks 
was recorded in a diagram drawn to scale. From these sections measure- 
ments were made and the areas occupied by the different types of cortex 
definitely mapped out. 
4. Histology of the Cortex. 
A. Neopallium . — The cerebrum of the guinea-pig is triangular in out- 
line and of very smooth contour. There are three fissures, which occupy 
much the same position as the fissures described in the brain of the rabbit 
by Mann (27). From the fact that they coincide so exactly in shape and 
position, the same nomenclature as that used by Mann has been adopted. 
The fissures are. 
1. The rhinal fissure. 
2. The Sylvian fissure. 
3. The pre- and post-lateral fissures of the rabbit form one continuous 
fissure — the lateral fissure. 
The histological examination of the cortex of the cerebrum led to the 
differentiation of five different types of cell lamination. The areas occupied 
by the different types are shown on the accompanying diagrams 1 and 2. 
The admirable method used by Mott has been adopted in demarcating 
these areas. Drawings of the cell lamination in the different areas which 
are shown in figures 3 to 8 were made by a camera lucida method devised 
by Dr G. H. Clark. 
