760 



DISSECTION OF TH1-] H!!,UX. 



roof; 



and floor. 



Septum 

 lucidum : 



position, 



form, and 

 attach- 

 ments ; 



is a double 



partition, 



containing 



fifth 



ventricle. 



Dissection. 



Fifth 

 ventricle. 



Dissection. 



Fornix 



position and 

 form. 



Upper sur- 

 face and 

 borders. 



a curve with the convexity outwards. In the roof are contained the 

 fibres passing from the hinder end of the corpus callosum down- 

 wards and outwards into the temporal lobe, together with the pro- 

 longation of the caudate nucleus and the toonia semicircularis ; and 

 at the anterior extremity is a prominence called the amygdaloid 

 tubercle. The floor is formed mainly by a long curved eminence 

 the hippocampus major (Z), along the inner margin of which is a 

 thin band prolonged from the fornix the tseiiia hippocampi (d\ 

 while to its outer side lies the tapering fore part of the eminent ia 

 collaterals (&). The choroid plexus (h) is continued downwards 

 along the inner side of the tseiiia hippocampi to the lower extremity 

 of this cornu. 



Dissection. If the student has a separated hemisphere and 

 opens the descending horn of the lateral ventricle as already 

 described, he will be able, by placing the handle of the scalpel in 

 the dentate fissure below, to demonstrate that the hippocampus 

 major is an infolding of the brain wall corresponding to that hollow. 



The SEPTUM LUCIDUM (figs. 274, 275, 6) is placed vertically 

 between the two lateral ventricles, beneath the anterior half 

 of the corpus callosum, to which its upper border is attached. 

 It is triangular in shape, with the base turned downwards and 

 forwards, and fixed to the rostrum of the corpus callosum. The 

 posterior border is oblique, and joins the fornix. Its surfaces look 

 into the lateral ventricles, opposite the head of the caudate nucleus. 

 Although often so thin as to be translucent, the septum lucidum 

 consists of two laminae which enclose a space the fifth ventricle. 

 Each lamina is composed of white substance, with a thin layer of 

 grey matter internally ; and the ependyma of the lateral ventricle 

 covers its outer surface. 



Dissection. The fifth ventricle will be exposed by cutting 

 through the piece of the corpus callosum which remains in the 

 middle line, and detaching the anterior half from the septum 

 lucidum. 



The FIFTH VENTRICLE (vent, of the septum) is a narrow slit 

 in the fore part of the septum lucidum, where this is deeper. 

 Posteriorly and above, the laminae of the septum are united to a 

 variable extent. Like the septum, it is larger in front than behind. 

 This cavity has not any epithelial lining. 



Dissection. The fornix is to be next examined. To lay bare 

 this body the posterior part of the corpus callosum should be 

 detached with care from it, and thrown backwards ; and the septum 

 lucidum should also be removed from its upper surface. 



The FORNIX (fig. 275, c) is a thin white layer beneath the corpus 

 callosum, which, projecting on each side into the lateral ventricle, 

 forms part of the floor of that cavity. Its central part or body is 

 triangular in shape, with the base turned backwards ; and it is con- 

 tinuous with the rest of the brain by processes named crura, or 

 pillars, in front and behind. 



The upper surface of the body has the septum lucidum attached 

 to it along the middle line in front ; and behind, its median part 



