16 



LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



median wall of the hemispheres demands our especial attention. 

 That this wall along its ventral border is everywhere continuous 

 with the epithelium of the choroid plexus has already been 

 shown. This condition is not changed when it is carried down- 

 ward along with the curving temporal lobe. From the base of 

 the embryonic terminal lamina to the tip of the temporal lobe 

 this border passes in a curve, marking the location of the fornix. 

 In the anterior portion of the brain, somewhat dorsad of the 

 fornix, the fibres of the corpus callosum are developed, evidently 

 from a portion of the embryonic lamina terminalis. They pass 

 across from one hemisphere to the other in a line which forms an 

 acute angle with the fornix. The substance between the two, 



SteUe wo Vordcrliint 

 and Imischenhim 

 zusarnmcnstossen. 



FIG. 8. 



FIG. 7. 



FIG. 7. Brain of a human embryo of the fourth month. 



FIG. 8. Inner aspect of the embryonic hemisphere, shown in Fig. 7. Shows the inner 

 lower border of the hemisphere, which becomes thickened into the wliite medullary 

 line of the fornix. The latter, however, only becomes medullary after birth. 



Stflle ico Vurderhirn und Zwischentiirn zusanimenslosnen, Point where the fore-bruin and mid-brain meet. 



which, of course, consists of the two thin layers of the primary 

 division-wall between the hemispheres, is the septum pellucidum. 

 These are important points, which I beg you to study carefully 

 in the accompanying figures. 



In the section shown in Fig. 9 you will observe an ana- 

 tomical structure not before mentioned. On the floor of the 

 cerebrum lies a thickening of the same, which projects, free, into 

 the ventricle,- the corpus striatum. That layer of the brain- 

 wall which later, as cortex, gives rise to the fibres of the cere- 

 brum, has already begun to appear. You see that an analogous 

 layer is present in the corpus striatum. In fact, in the adult 

 animal nerve-fibres originate there just as in the cortex. 



