1890 - 91 .] Alexander Bruce on a Human Cyclops. 
415 
presence of the corpus callosum, fornix, or septa lucida, and there 
was, consequently, no differentiation of the lateral from the third 
ventricles. At the bottom of the shallow longitudinal fissure the 
two hemispheres were connected by white brain substance about 
one-quarter of an inch in thickness, hut this did not present any 
of the characters of the corpus callosum. A peculiar structure com- 
posed of cerebral substance, whose relationships were not at first 
apparent, was found in the interior of the single ventricular cavity. 
It extended almost to the anterior extremity of this cavity, and 
appeared to be formed of an invagination of the posterior wall of 
the cerebral mantle. Fig. 5 shows the appearance of this structure 
as seen from its anterior aspect. It had the shape of a horse-shoe, 
the ends pointing downwards and being attached to the cerebral 
substance at a level slightly below that at which the section was 
made. The anterior margin was rounded, and on its surface 
numerous vessels ramified. Fig. 6 shows the appearance of this 
structure as seen from behind. The dark space v. represents that 
part of the ventricular system continued backwards underneath 
the cavity of the horse-shoe-shaped structure, which must, I think, 
he considered as the equivalent of the third ventricle, while the 
narrow slit l.v. seen on the left side points to the hinder extremity 
of the part of the ventricular system superior to the arched 
structure which may be regarded as the lateral ventricle. 
Between the dark slits marked v. and l.v. are two curved bands 
or laminse of white matter, convex backwards. The anterior or 
narrower of these bands is separated from the posterior or broader 
band by a narrow convex space. This interval was occupied by a 
little vascular connective tissue. Both laminae at their outer 
extremities passed into the substance of the hemispheres. Examina- 
tion of a series of microscopic sections indicated that the upper 
and lower laminae became continuous round the anterior margin of 
the horse-shoe-shaped structure depicted in fig. 5, while the inferior 
laminae at its extremities became fused with the rudimentary basal 
ganglia. The relationships of this peculiar structure seemed to me 
to indicate that it had been formed in the same way as the velum 
interpositum of the normal brain, namely, by an ingrowth of 
vascular connective tissue of the pia mater carrying before it a 
duplicature of the posterior cerebral wall, but that, contrary to what 
