DEVELOPMENT OF THE BRAIN. 



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connected by means of the foramen of Monro, which at the 

 earlier periods is very wide, but subsequently becomes narrowed 

 to a mere slit. The cerebral hemispheres are separated by the 

 ingrowth of a septum, which is ultimately formed into the falx 

 cerebri. The hemispheres are then greatly enlarged in the back- 

 ward direction, so that they quite overlap the thalamencephalon 



Diagram of a horizontal section of a vertebrate brain. (Huxley;. Off. Olfactory lobes. 

 L.t. Lamina terrainalis. C. V. Corpus striatum. 2%. Optic thalaraus. Pn. Pitieal gland. 

 M.b. Mid-brain. Cb. Cerebellum. M.O. Medulla oblongata. 1. Olfactory ventricle. 2. 

 Lateral ventricle. 3. Hind ventricle. 4. Fourth ventriele. + Iter a tertio ad quartum 

 ventriculum. 



and the parts developed from the middle cerebral vesicle. The 

 corpus callosum is subsequently formed by the fusion of the juxta- 

 posed parts of the hemispheres. 



From the anterior part of the cerebral hemispheres arise two 

 prolongations, which develop into the olfactory bulbs, these grow 



