174 ANATOMY OF THE CENTEAL NEETOUS SYSTEM. 



Hence it seems to me the most important result under consideration 

 up to the present time, that we have been able to demonstrate that the first 

 cortical area developed in the animal kingdom was the olfactory cortex. The 

 olfactory cortex is the cortex of the dorso-median area, because just this area 

 is where the fibers from the terminus of the secondary olfactory tract end. 

 A clew which could throw light on the functional significance of other cor- 

 tical areas in reptiles has not been found. They may belong to the olfactory 

 apparatus, but not necessarily so. 



That the oldest cortex represents essentially only a single sensory center 

 — the olfactory center; that all associations which serve them as a founda- 

 tion, all memory-pictures which they retain, are such as serve especially the 

 sense of smell; these facts furnish a point of departure for new investiga- 

 tions in the field of comparative psychology. Studies in animal psychology 

 have, up to the present time, been based upon too complicated psychic 

 phenomena. We must first know what sensory impressions a lower animal 

 may receive, what it may retain, and how far — directly or through associative 

 thought — it is able to interpret these impressions. Then only shall we be 

 prepared to approach the complicated problems which have tisually been 

 attempted. 



Let us now turn back to the purely morphological considerations, and 

 determine first how, in the course of the vertebrate series, other tracts have 

 been associated with the cortical olfactory tracts; how the complicated 

 apparatus which we see in the mammalian brain came to be. 



Unfortunately there is not much that can be reported. There are 

 evervAvhere gaps in our knowledge, everywhere it requires more diligent 

 collaboration in the field only recently discovered. 



We have set aside the olfactory center while we studied the connections 

 which joined the olfactory apparatus with the cortex. Though we may not 

 find with certainty also in reptiles another and similar connection, we may 

 turn to the avian brain, which will furnish a number of other bundles con- 

 necting the cortex with parts of the brain lying farther back. 



Most interesting to me from the stand-point of comparative psychology 

 is the bundle which arises in the occipital region of the brain, passes forward 

 to bend sharply downward and backward, and thence passes to the termini 

 of the optic nerve in the midbrain. The Tr. Occipito-mesencephalicus is so 

 enormously developed in the pigeon that it appears to be one of the very 

 largest bundles of the whole brain. The reptiles possess, apparently in the 

 same location, a thin bundle; it is not, however, absolutely certain^ A 

 pigeon in which one has severed this bundle appears to be blind in the eye 

 on the side opposite the severed bundle, taking its bearings with difficulty 

 and always with the eye that has the uninjured central visual field. We 

 know that up to mammals and man there exists such a tract from the 



