190 TOPOGRAPHICAL ANATOMY OF THE 



investment, the ependyma,^ continuous with that lining the whole 

 of the interior of the ventricle. Parallel to, and partially covered by, 

 the choroid plexus is the edge of the fornix and its backward 

 continuation, the fimbria hippocarajpi. The last named is a white hem 

 applied to the rounded, elongated eminence, the hippocaynpus,- which 

 extends from the floor of the central part of the ventricle down the 

 inferior cornu to the piriform lobe. The deeper part of the hippocampus 

 is grey in colour, but its ventricular surface is covered by a layer of 

 white fibres, the alveiLs,^ derived from the crus of the fornix. 



The anterior cornu (cornu anterius) of the ventricle is, strictly 

 speaking, merely an extension of the central part beyond the interven- 

 tricular foramen. It inclines in a ventral direction and is continuous, 

 through a narrow canal, with the cavity of the olfactory bulb. 



The inferior cornu (cornu inferius) is a tapering and curved pro- 

 longation of the ventricle into the piriform lobe, where it ends on a level 

 with the point at which the optic tract makes its appearance on the 

 surface of the brain. The cornu contains the tail of the caudate nucleus 

 (cauda nuclei caudati) reduced to a slender grey ridge, and the 

 diminished continuations of the choroid plexus, fimbria and hippo- 

 campus. 



The septum pellucidum is a thin, medial partition that separates 

 the anterior part of the pars centralis of the two ventricles, and fills the 

 triangular gap between the corpus callosum and the fornix. It is com- 

 posed of two thin laminae in contact with each other, and is thickest near 

 the columns of the fornix. 



Dissection. — The fornix must now be exposed as completel}^ as the 

 present stage of the dissection permits. Cut across the remains of the 

 corpus callosum about the genu, and remove it from this point to the 

 splenium. Its connection with the septum pellucidum is necessarily 

 destroyed in the operation. 



The hemi-sected brain affords much assistance in the study of the 

 fornix, which there appears as a curved white band, ventral to the corpus 

 callosum. 



Fornix. — The fornix * consists of two bands of fibres pursuing an 

 arched course and intimately connected with each other at one place. 

 The fibres are mainly longitudinal in direction and connect structures 

 on the same side of the median plane ; but there are also some commis- 

 sural fibres that unite the two hippocampi (commissura hippocampi). 



The hody of the fornix (corpus fornicis) consists of the fused right 



1 eTrii>5vfj.a. (epeiidyiiia) [Gr.], an outer garment. 



2 [■KwoKd.fj.TToz (hippocampos) [Gr.], a monster, with a horse's body and a fish's tail, on 

 which the sea-gods rode (named from its sliape in the human brain). 



^ Alveus [L.], a hollow vessel, a tub, a tray. 

 * Fornix [L.], an arch or vault. 



