XXX.] THE BRAIX. 310 



The space between the cortex and the mid -brain 

 in which lies the velum interposition is the so- 

 called transverse fissure. 



17. In the median line cut through the fornix, with 

 the posterior part of the corpus callosum which 

 remains attached to it ; 



Note that the cortex curls a short way under- 

 neath the corpus callosum. 



18. On one side pull the fornix and hippocampus 

 backwards ; note on the outer (lower) surface of 

 the cortex, the dentate or hippocampal fissure; 

 it is shallow and is situated a short distance from 

 the edge of the fimbria, nearly opposite the 

 middle of the hippocampus; it runs from the 

 cortex underneath the corpus callosum (cp. 17) 

 to the extremity of the cortex of the descending 

 cornu of the lateral ventricle ; the projection of 

 the hippocampus seen in the descending cornu 

 is caused by the folding of the cortex round 

 this fissure ; note the lower surface of the pos- 

 terior pillars of the fornix. 



19. Turn back the velum interpositum ; in separa- 

 ting the velum posteriorly note two projections 

 downwards into the median space, these are the 

 choroid plexuses of the third ventricle. 

 The optic thalamus will now be seen on each 

 side, a depression runs round its lateral boundary; 

 between the optic thalami is a narrow space, the 

 third ventricle. Note the tail of the nucleus 

 caiulatus stretching backwards for some distance 

 laterally of the optic thalamus. 



