THE BEAIN AND SPINAL CORD. 211 



mpus buried in the hippoeainpal fissure. The longitudinal 

 •iae, the thin layer of grey matter on the upper surface of the 

 rpus callosum, and the grey matter on the fornix, are also 

 rived from the primitive callosal gyrus. 



(4) The lamina terminalis is seen in section. It is the 

 rminal anterior wall of the fore-brain (Fig. 171). The lower 

 ,rt becomes the lamina cinerea ; in the upper part, the anterior 

 mmissure is developed, and the anterior pillars of the fornix 

 ig. 172). Its dorsal extremity bounds anteriorly the foramina 



Monro. It connects the mesial walls of the cerebral vesicles 

 'ig. 171), and becomes thickened and enlarged. In its dorsal 

 ,rt, where it is continuous with the primitive callosal gyrus, 

 e callosal commissure (corpus callosum) commences. The 

 irt of the lamina terminalis which lies between the fornix 

 id corpus callosum (Fig. 172) forms the septum lucidum. In 

 is septum a cavity appears — the 5 th ventricle. Cases are 

 lown of people with normally functional brains in which the 

 rpus callosum was found afterwards to be absent. 



The corpus callosum connects the cortex of one hemisphere 

 ith the basal ganglia and cortex of the other. It is the 

 mmissure of the neo-pallium. Its fibres are probably collaterals 

 srived from the pyramidal and other fibres of the cortical 

 Us. Each fibre grows out and crosses the great median 

 sure of the brain in the lamina terminalis. 



The Fornix is developed in the inner margin of the primitive 

 llosal gyrus, which bounds the transverse or choroid fissure 



'ig. 171). 



The Corpus Striatum. — As soon as the cerebral vesicle grows 

 it, the corpus striatum appears as a thickening in its wall at 

 e outer side of the foramen of Monro (Fig. 173). With the 

 isterior development of the vesicle it comes to lie in the ven- 

 ieular floor, from the foramen of Monro to its posterior 

 tremity. 



The anterior extremity of the corpus striatum is continuous 

 ith the olfactory lobe (Fig. 173). Hence in the adult brain 

 e anterior end of the corpus striatum appears at the base of the 

 ain in the anterior perforated space, a lamina of grey matter 

 rived from the olfactory lobe (Fig. 18, p. 22). As the cerebral 

 side grows over the optic thalamus (Fig. 173) the corpus 



