536 THE NERVOUS SYSTEM. 
ventricle. It les on the surface of the hippocampus major and is continuous 
behind the posterior part of the optic thalamus, with the choroid plexus in the body 
of the lateral ventricle. But it must not be supposed that the choroid plexus les 
free in the ventricular cavity. It is clothed in the most intimate manner by an 
epithelial layer, which represents the inner or mesial wall of the descending horn 
Caudate nucleus 
Lenticular nucleus 
Anterior commissure 
Genu of corpus callosum 
Septum lucidum 
Ventricle V. 
Caudate nucleus 
Foramen of Monro 
Teenia semicircularis 
Optic thalamus 
Fornix 
Mesial longitudinal stria on the 
splenium of the corpus callosum 
Fic, 398.—DIssEction, to show the fornix and the posterior and descending cornua 
of the lateral ventricle of the left side. 
pushed into the cavity by the choroid plexus. The ventricle, therefore, only opens 
on the surface through the choroid fissure when this thin epithelial layer is torn 
away by the withdrawal of the choroid plexus. From the above, it will be under- 
stood that the arcuate choroid fissure, throughout its whole length (viz. from the 
foramen of Monro to the extremity of the descending horn of the lateral ventricle), 
is formed by the involution of a portion of the wall of the hemisphere which 
remains epithelial. In the body of the ventricle this layer is attached, on the one 
hand, to the sharp lateral margin of the fornix, and on the other to the upper 
surface of the optic thalamus; in the descending horn it is attached, in like manner, 
to the edge of the fimbria or posterior pillar of the fornix, whilst above it joins the 
roof of this portion of the ventricle along the line of the teenia semicircularis. 
The eminentia collateralis shows very great differences in its degree of develop- 
ment, and it may present two distinct forms, which may be distinguished from 
each other as the eminentia collateralis posterior and the eminentia collateralis 
anterlor. 
The posterior collateral eminence is a smooth elevation in the floor of the 
trigonum ventriculi, in the interval which is left between the calcar avis and the 
hippocampus major as they diverge from each other. In the feetal brain this is 
ee 
