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(not of the primary neural axis) and the other four parts of the hemi- 

 sphere are so related that the two ventral parts correspond with and 

 pass back directly into the ventral or motor lamina of the lower parts 

 of the neural tube, visceral efferent functions predominating in the 

 ventro-median part and somatic efferent in the ventro - lateral part. 

 The two dorsal parts of the hemisphere correspond with the dorsal 

 or sensory lamina of the neural tube, but direct continuity between 

 the telencephalic and diencephalic segments of the dorsal lamina is 

 interrupted in forms above the fishes by the great di-telencephalic 

 fissure and (in Amniota) the posterior chorioidal fold. 



Primitively the evaginated cerebral hemisphere was simply a pri- 

 mary and secondary olfactory center. In very early phylogenetic 

 stages ascending fibers entered this secondary olfactory center from 

 the pars dorsalis thalami for olfacto-tactile correlations etc., and from 

 the hypothalamus for olfacto- visceral correlations; and as we ascend 

 the phylogenetic series this non - olfactory correlation tissue assumes 

 relatively greater importance. So far as this tissue serves simple 

 stereotyped reflexes it is developed in the ventral part of the hemi- 

 sphere — the visceral centers medially and the somatic centers later- 

 ally. The olfactory component of the latter center plays progressively 

 a smaller part in higher animals until this tissue becomes the true 

 corpus striatum. While the ventral parts of the hemisphere are there- 

 fore favorably situated to serve simple, rapid stereotyped reflexes, the 

 dorsal parts of the hemisphere (pars pallialis, Gaupp), not being in 

 direct connection with the corresponding diencephalic and lower re- 

 gions of the brain in forms above fishes, are not well adapted for 

 these rapid responses but rather for the slower and more complex 

 discriminative reactions and (in higher animals) intelligent acts. Thus 

 the two dorsal parts are in the course of the phylogeny gradually 

 transformed from secondary olfactory nuclei into true cortex cerebri. 

 Both dorsal parts continue throughout the phylogeny to receive some 

 olfactory fibers, but these are much more numerous in the dorso- 

 lateral part, which forms the pyriform lobe. Accordingly the latter in 

 all mammals is more like the primordial secondary olfactory tissue 

 than are the other parts of the pars pallialis. 



Since the dorso-medial part of the hemisphere is to a less extent 

 under the direct domination of any single one of the functional systems 

 which enter into the cerebral hemisphere, in it the higher correlation 

 tissue was first developed. The preponderating element at first in 

 this pallial correlating apparatus was undoubtedly olfaction. Never- 

 theless cerebral cortex is not developed under the influence of any 



