THE CEREBRUM 439 



mater, which is prolonged, into the inferior horn and the 

 central part of the lateral ventricle, through the chorioid fissure 

 of the cerebrum. In the inferior horn it lies on the surface 

 of the hippocampus and, at the posterior extremity of the 

 thalamus, it becomes continuous with the chorioid plexus in 

 the central part of the lateral ventricle (Fig. 166). But it 

 must not be supposed that the chorioid plexus lies free in 

 the ventricular cavity. It is clothed in the most intimate 

 manner by an epithelial ependymal layer, which represents 

 part of the original medial surface of the hemisphere pushed 

 into the cavity by the chorioid plexus. The ventricle, there- 

 fore, opens on the surface through the chorioid fissure only 

 after the thin epithelial layer is torn away by the withdrawal 

 of the chorioid plexus. 



Eminentia Collateralis. The collateral eminence is some- 

 times separated into two parts, which may be distinguished 

 from each other as the eminentia collateralis posterior and 

 the eminentia collateralis anterior (Figs. 166, 171). 



The posterior collateral eminence is a smooth elevation in 

 the floor of the trigonum collaterale, in the interval between 

 the calcar avis and the hippocampus as they diverge from 

 one another. The anterior collateral eminence is not always 

 present. It forms an elongated elevation in the floor of the 

 inferior horn of the lateral ventricle, to the lateral side of 

 the hippocampus. Both eminences correspond to the col- 

 lateral fissure on the inferior aspect of the cerebral 

 hemisphere. 



Dissection. The dissector should now detach the remains 

 of the right temporal lobe and of the right occipital lobe from 

 the rest of the cerebrum by cutting through the forceps major 

 of the splenium of the corpus callosum and through the fimbria 

 where it passes into the crus of the fornix. The knife should 

 then be carried forwards from the anterior extremity of the 

 inferior horn, above the level of the uncus, through the temporal 

 pole. The temporal lobe, including the hippocampal gyrus 

 along its medial side, can then be separated from the remainder 

 of the brain, along the line of the chorioid fissure of the cerebrum. 

 In the detached part of the cerebrum (Fig. 171) a good view is 

 obtained of the floor of the inferior horn and of the parts in 

 relation to it. Further, by replacing it in position, the dissector 

 will be better able to understand the chorioid fissure, and by 

 turning the brain upside down he will obtain a view of the roof 

 of the inferior horn and the structures in relation to it. In that 

 way the tail of the caudate nucleus and the stria terminalis can 

 be traced into the amygdaloid nucleus. 



The cut edge of the central part of the corpus callosum, which 

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