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INTRODUCTION TO NEUROLOGY 



The olfactory cerebral centers fall into two groups: (1) the 

 reflex centers of the brain stem and (2) the olfactory cerebral 

 cortex. The arrangements of the olfactory reflex centers and 

 their connecting tracts are essentially similar in plan in all ver- 

 tebrate brains (except in some aquatic mammals, like the dol- 

 phin, which lack olfactory organs altogether). The olfactory 

 cerebral cortex, on the other hand, is very diversely developed 

 in different groups of vertebrates. There is no true cerebral 

 cortex in fishes; in amphibians (particularly in the frog) the 

 olfactory cerebral cortex begins to emerge from the general 



Fig. 103. Dissection of the right olfactory bulb and nerve on the 

 lateral wall of the nasal cavity. (From Wood's Reference Handbook of the 

 Medical Sciences.) 



olfactory reflex centers; in reptiles there is a well-formed olfac- 

 tory cortex of simple histologic pattern and the beginnings of the 

 non-olfactory cortex; in birds the olfactory apparatus is reduced 

 and the non-olfactory cortex is somewhat more extensive than 

 in reptiles; in mammals both the olfactory cerebral cortex and 

 the non-olfactory cortex attain their maximum dimensions, the 

 former in the lowest members of this group and the latter in the 

 highest. 



The cerebral cortex as a whole is sometimes called the 

 pallium. That portion of the pallium which is related with the 

 olfactory apparatus was differentiated earlier in vertebrate evo- 



