MORPHOLOGY OF THE FOREBRAIN 489 



possible when the internal structure of the reptilian brain is more 

 fully known. It is probable (see above, p. 464) that here the ventral 

 margin of the dorso-median cortex is morphologically and physio- 

 logically very similar to the mammalian hippocampus; and that 

 the cortex lateralis, which differentiates over the striatum- 

 epistriatum complex and within the sphere of influence of the 

 lateral olfactory tract, stria medullaris and lateral forebrain 

 tract (tr. strio-thalamicus),is comparable with the pyriform lobe 

 with neopallial (somatic sensory) factors predominating. But 

 the fact that in Lacerta fibers arising from all parts of this cortex 

 pass by way of the fimbria into the commissura hippocampi and 

 fornix (Ramon y Cajal, '04, fig. 852, p. 1103) suggests that, 

 though the reptilian differentiation is far in advance of the am- 

 phibian, nevertheless the localization of cortical function is still 

 very imperfect in reptiles and the terms hippocampal cortex and 

 neopallial (somatic) cortex, if used at all, must be employed with 

 the same reservations made above in our discussion of the amphi- 

 bian pallium, i.e., as designations of spheres of predominant 

 olfactory and non-olfactory sensory-motor coordination within 

 a common matrix. 



We conclude, then, that the distinction between neopallium 

 and archip allium (hippocampal formation), while valid physio- 

 logically and histologically in higher brains, does not rest upon a 

 difference in the time of their first appearance, for the primordium 

 of the archipallium is not older than that of the neopallium. The 

 earliest primordia of the cerebral cortex performed both functions. 

 Nevertheless, since the olfactory function clearly predominated in 

 this complex in its early phylogeny and since (in correlation 

 with the last point)in Ichthyopsida this primordium occupies the 

 morphological position of the mammalian hippocampus, it is 

 permissible to speak of the common cortical Anlage as primordium 

 hippocampi. Moreover, there is no question that the hippocampal 

 formation reached its full functional maturity earlier in the phy- 

 logeny (viz., in the lowest mammals) than did the neopallium, 

 which is apparently now in process of further evolution in the 

 human race. On this ground the term neopallium is justified, 

 even though its simple primordia may be as old as those of the 

 hippocampus. 



