682 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



convex surface of the hemisphere. 1 Ferrier 2 from the study of monkeys em- 

 phasizes the importance of the cortex of the angular gyrus ; but these various 

 results must ultimately be harmonized through studies of degeneration in man 

 and the monkeys which will show the relative values of the several parts, all 

 of which are in some degree involved. 



First Nerve. Comparative anatomy indicates that the parts of the en- 

 cephalon mediating the sense of smell are most closely connected with the 

 cerebral hemispheres, in the sense that phylogenetically the first development 

 of the hemispheres was in connection with the central terminations of the 

 olfactory tracts. 3 It happens in man, however, that although the cerebral hem- 

 ispheres are proportionately much more massive than in the lower mammals, 

 yet the olfactory bulbs and tracts are at the same time but poorly developed. 

 The pathway of the olfactory impulses is from the olfactory area in the nose 

 to the olfactory bulb of the same side, thence via the olfactory tract to its 

 termination in front of the anterior perforated space, one branch of the tract 

 passing directly into the substance of the gyrus fornicatus at this point, and 

 the other going into the more lateral portion represented in man by the tem- 

 poral end of the gyrus hippocampi. The cortical areas, together with the 

 olfactory lobe and tract, form the rhiuencephalon of the comparative anat- 

 omists. It has been shown, nevertheless, by Hill 4 that in anosmic mammals 

 the fascia dentata alone varies with the development of the olfactory apparatus. 

 The experimental pathological evidence is very meagre in relation to these 

 nerves, but, on the other hand, the anatomical evidence is of the best. 



The brief sketches of the pathways for incoming impulses indicate that 

 with the exception of those coming by the olfactory tract, they arrive ulti- 

 mately at the cerebral cortex over the fibres forming the internal capsule, 

 most, if not all, passing by way of the thalamus. In the cerebral cortex are 

 found the terminal branches of the last cell-groups furnishing neurons which 

 conduct toward the cerebrum, and these are arranged in several layers corre- 

 sponding to the various strata of fibres which the cortex always shows. 



F. LOCALIZATION OF CELL-GROUPS IN THE CEREBRAL CORTEX. 



The foregoing section has brought to light the fact that groups of incom- 

 ing impulses find their way to the cerebral cortex. The path to the cerebrum 

 is best developed in the higher animals. In any case, the impulse in order to 

 produce evident responses must finally escape from the central system into the 

 tissues controlled, and using the reactions of the expressive tissues as a guide, 

 it is our present purpose to trace the impulses in those cases in which the cor- 

 tex forms part of the path. We turn, therefore, to the study of those parts 

 of the cerebral cortex the direct stimulation of which produces impulses that 

 pass to cell-groups lying more or less caudad in the central system. 



1 Donaldson : American Journal of Psychology, 1892, vol. iv. No. 4. 



2 The Oroonian Lectures on Cerebral Localization, London, 1890. 



3 Sir William Turner : Journal of Anatomy, 1890 ; Edinger : Anatomische Anzeiger, 1893. 



4 Philosophical Transactions of the Royal Society, 1893, vol. clxxxiv. 



