CHAPTEE X 



THE FORE-BRAIN 



CONTENTS. 1. General anatomy of telencephalon. 2. Structure of the cerebral 

 cortex or pallium. 3. History of cerebral localisation. 4. Excitable zone of the 

 cerebral cortex ; localisation in dog, monkey, man. 5. Physiological analysis of 

 motor reactions of cerebral cortex. 6. Inhibitory reactions. 7. Organic reactions 

 of cortical origin. 8. Epilepsy from cortical excitation. 9. The sensory-motor 

 area, deduced from effects of partial or total destruction of excitable cortex. 10. 

 Functions of basal ganglia or corpora striata (caudate and lenticular nuclei). 

 11. Visual area. 12. Auditory area. 13. Olfactory and gustatory areas. 14. 

 Association areas ; division of cortex into thirty-six areas, according to Flechsig's 

 embryological method. 15. Physiological analysis of speech disorders of cerebral 

 origin. 16. General theory of the psycho - physical functions of the brain. 

 Bibliography. 



I. THE Fore-brain (prosencephalon, telencephalon, brain proper) 

 represents in man, as in all vertebrates, the most bulky segment of 

 the central nervous system. It originates in the primary cerebral 

 vesicle, from which at an early stage the two diverticuli, which are 

 known in the adult as the lateral ventricles, develop, while the 

 central portion of the vesicle is reduced to the small cavity of the 

 third ventricle. The walls of this cavity develop progressively in 

 the vertebrate series, and become the cerebral hemispheres. 



The primary vesicle thickens at the base, where a large mass, 

 which embryologists call the basal lobe, develops. Its anterior 

 portion, from which the fibres of the olfactory nerve emerge, is 

 destined to constitute the olfactory apparatus ; the posterior part 

 is of a considerable size, and forms the so-called corpus striatum. 

 These masses are afterwards separated by a fissure from the more 

 conspicuous segment of the vesicle, the walls of which ^thicken 

 comparatively late, and form the mantle of the brain or pallium. 

 Fig. 260 is a good representation of the several parts or segments 

 of the human brain in its early period of development. Its various 

 parts are more or less developed in all mammals, both during 

 embryonic life and after development has been completed. 



In the bony fishes the pallium is represented merely by an 

 epithelial layer ; in the cyclostomes the side walls alone begin to 

 thicken; in certain species of selachians an enlargement takes 



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