272 



THE NERVOUS SYSTEM 



is not very evident in the human brain, but can be easily dissected out in the 

 sheep (Fig. 204). 



The columns fornicis are round fascicles which can be traced ventrally in 

 an arched course to the mammillary bodies (Figs. 203-205). They are placed 

 on either side of the median plane. Each consists of an initial free portion, 

 which forms the rostral boundary of the interventricular foramen, and a cov- 

 ered part, which runs through the gray matter in the lateral wall of the third 

 ventricle to reach the mammillary body (Figs. 204, 205). 



The relations of the fornix are well shown in Figs. 155, 200, and 205. The 

 body of the fornix intervenes between the corpus callosum, septum pellucidum, 



Body of corpus callosum 



Lateral ventricle 

 Genu of corpus callosum 



Body of fornix 



Hippocampal commissure 

 ! Thalamus 



Splenium of corpus callosum 

 . Lateral ventricle 



Chorioid fissure 

 Hippocampus 



Anterior commissure 



- Fimbria of hippo- 

 campus 

 -W- Hippocampal 



fissure 



-/- Hippocampal gyms 

 ^^^r^ 



' Dentate fascia 



Mammillothalamic tract 

 Mammillary body 

 Infundibulum 



Fig. 204. Dissection of the cerebral hemisphere of the sheep to show the fornix and hippocampus. 



Median view. 



Lamina terminalis 



Optic chiasma \ 



Column of fornix. 



and cavity of the lateral ventricle on the one hand, and the transverse fissure of 

 the cerebrum and the thalamus on the other. The fimbria and body of the for- 

 nix form one boundary of the chorioid fissure. This fissure, which is shown but 

 not labeled in Fig. 205, represents the line along which the chorioid plexus is 

 invaginated into the lateral ventricle. When this plexus has been torn out, 

 the fissure communicates with the interventricular foramen. 



The septum pellucidum is the thin wall which separates the two lateral ven- 

 tricles and fills in the triangular interval between the fornix and the corpus 

 callosum (Fig. 205). It consists of two thin vertical laminae separated by a 

 cleft-like interval, the cavity of the septum pellucidum (Fig. 177). Each lamina 



