388 DISSECTION OF THE BABBIT. 



and floor of the anterior part of the lateral 

 ventricle. It lies in front of the hippocampus 

 major, from which it is separated by a deep 

 groove, running obliquely backwards and out- 

 wards across the floor of the ventricle. 



Cut away carefully the outer wall of the anterior conm 

 of the lateral ventricle, including the corpus striatum. 



vi. The septum lucidum, is the thin vertical inner 

 • wall of the hinder part of the anterior cornu. 

 It is placed opposite the corpus striatum, and 

 ventral to the corpus callosum. 



vii. The foramen of Monro is a small hole imme- 

 diately beneath the hinder border of the septum 

 lucidum, through which the lateral ventricle 

 communicates with the third ventricle, or 

 cavity of the thalamencephalon. 



viii. The posterior pillar of the fornix is a narrow 

 band, lying along the anterior edge of the 

 hippocampus major. Posteriorly it follows 

 the hippocampus into the descending cornu ; 

 while anteriorly it becomes continuous with 

 its fellow of the opposite side in the median 

 plane, forming the body of the fornix, imme- 

 diately above the foramen of Monro. 



ix. The choroid plexus is a thin vascular fold of 

 the inner wall of the hemisphere, projecting 

 into the descending cornu in front of the 

 hippocampus major, and closely applied to the 

 anterior surface of the latter along its whole 

 length. 



X. The ' fifth ventricle ' is a median vertical cleft 

 between the right and left hemispheres. It 

 lies below the corpus callosum and above the 

 fornix, and is bounded laterally by the inner 

 walls of the two hemispheres (septum lucidum). 

 It is merely a part of the space between 



