THE FORNIX. 7'H 



is united to the corpus callosum. Each border is free in the 

 -Bonding lateral ventricle, where it rests on the optic thalamus, 

 the velum interposituni being between the two ; and along it lies 

 the choroid plexus. Posteriorly it joins the corpus callosum in the Posterior 

 middle, while on each side it sends off a small riband-like band aE 

 the posterior pillar or tcenia hippocampi (fig. 276, c, p. 763), along the 

 concave margin of the hippocampus major. At the anterior end anterior 

 it is arched over the foramen of Monro, opposite the front of the part ' 



thalamus, and ends likewise in two anterior pillars, which 

 will be afterwards followed downwards to the corpora albicantia 

 and thence into the optic thalami. 



If the fornix be cut across near its front, the foramen of Munro Under 

 will be opened, and the descending anterior pillars will be seen su 

 (fig. 276). When the posterior part is raised (and it must 

 bt- done with great care), it will be found to be supported on a 

 process of the pia mater, named velum interposituni. Posteriorly, 

 on the under aspect, is a triangular surface, marked by transverse is marked 

 lines, which are produced by the fibres of the corpus callosum y 

 appearing in the interval between the two diverging posterior 

 pillars of the fornix : the part which is so defined has been called 

 the lyra (fig. 276, ). 



The fornix may be described as consisting of two bands, right Fornix 

 and left, which are united for a certain distance in the central part JjJJ^nda 

 or body. According to this view, each band, commencing in the 

 optic thalamus and passing through the corpus albicans, arches over 

 the foramen of Monro, and after forming the body of the fornix, is 

 continued as the taenia hippocampi to the hook of the uncinate 

 convolution. 



The FORAMEN OF MONRO (fig. 274, p. 757) is a short slit Foramen of 



between the fore part of the fornix and the optic thalamus. Monro - 

 Through it the lateral ventricle communicates with the third 

 ventricle, and indirectly with the one of the opposite side. It is 

 lined by a prolongation of the ependyma, which is thus continued 

 from one ventricle to the other. 



The student may leave untouched for the present the velum 

 interpositum, and proceed to examine the bodies which have been 

 enumerated in the floor of the posterior and descending cornua. 



The HIPPOCAMPUS MINOR or CALCAR AVIS (fig. 275, i) is a spindle- Hippocam- 

 shaped prominence on the inner side of the posterior cornu of the 1>Us aor> 

 lateral ventricle. If it is cut across, it will be seen to be formed formed by 

 by the calcarine fissure pushing outwards the wall of the cavity, 

 and beneath the white layer is the cortical grey substance passing 

 from the uncinate convolution to the cuneate lobule at the bottom 

 of the fissure. 



The HIPPOCAMPUS MAJOR (figs. 275, I, and 276, 6) is the large Hippocam- 

 convex eminence in the fioor of the descending cornu of the lateral pus 

 ventricle, and, like that, is curved, with the concavity directed 

 inwards. Its anterior extremity, which is named the pes hippocampi, p e .s hippo- 

 is somewhat enlarged and presents two or three indentations, 

 resembling the foot of a feline animal. 



