494 THE BRAIN 



lateral ventricle (Fig. 200). 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 epen- 

 dymal layer, which represents the medial wall of the inferior 

 horn pushed into the cavity by the chorioid plexus. The 

 ventricle, therefore, opens on the surface through the chorioid 

 fissure only after this thin epithelial layer is torn away by 

 the withdrawal of the chorioid plexus. 



Eminentia Collaterally This eminence may present two 

 distinct forms, which may be distinguished from each other 

 as the eminentia collateralis posterior and the eminentia col- 

 lateralis anterior. 



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 

 each other. The anterior collateral eminence is not always 

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

 inferior horn "of the lateral ventricle, on the lateral side of 

 the hippocampus. Both eminences correspond to the col- 

 lateral fissure on the tentorial aspect of the cerebral 

 hemisphere. 



Dissection. The remains of the right temporal lobe and of the right 

 occipital lobe should now be detached from 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 anteriorly from the anterior extremity of the inferior 

 horn, above the .level of the uncus, through the temporal pole. The 

 temporal lobe, with the hippocampal gyms 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. 201) 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 

 chorioid fissure can be better understood, and by turning the brain upside 

 down a view is obtained of the roof of the inferior horn and the structures 

 in relation to it. In this 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 is still in 

 position, should now be still further pared away, so as to bring the sub- 

 jacent septum pellucidum and the fornix more fully into view. 



Fimbria (Figs. 200, 201). This is simply a continuation 

 of the crus (O.T. posterior pillar) of the fornix. It is a con- 

 spicuous band of white matter, which presents a prominent free 

 border. Anteriorly, it runs into the recurved extremity of 

 the uncus, whilst, if it is traced posteriorly, it will be seen 

 to curve upwards, posterior to the thalamus, and become 



