114 Bulletin of Laboratoiies of Denison Univa'sity [Voi. xiii 



the epistriatum in teleosts is a prophesy of the evolution of the 

 cortex cerebri in the later phylogeny. The olfactory and gus- 

 tatory tertiary tracts end together throughout the inferior lobe 

 and they have a common descending conduction path, the trac- 

 tus lobo-bulbaris. In addition to this ventral olfactory path, 

 there is the dorsal tertiary tract from the fore-brain to the hab- 

 cnula and its descending path of the fourth order, Meynert's 

 fasciculus retroflexus. This path offers opportunity for somatic 

 sensory (including optic) and somatic motor connections analog- 

 ous to those provided for the sense of taste in the inferior sec- 

 ondary nucleus. 



If the olfacto-gustatory connections of the human body are 

 at all similar to these of fishes, this relation offers a possible 

 anatomical correlate of the familiar fact of experience that sub- 

 jectively we distriminate tastes and smells only imperfectly, in 

 many cases not at all, without the aid of collateral physiological 

 experimentation to determine which organ receives the stimulus. 



It is freely granted that these comparisons are, in the pres- 

 ent state of our knowledge, rather fanciful. They are offered 

 merely as the first practicable working hypothesis for a correla- 

 tion of the olfactory with the other sensory mechanisms. If the 

 anterior end of the primary nerve tube lies in the region of the 

 preoptic recess, as seems to be now commonly assumed, the 

 peculiar relations of the rhinencephalon are to be explain- 

 ed as due to the suppression of the most anterior sensory and mo- 

 tor centers of other systems, leaving the olfactory apparatus free 

 to develop without constraint. 



The most striking difference noticeable in the diagram be- 

 tween the centers for taste and smell is the apparently ventral 

 position of the primary and secondary olfactory centers as con- 

 trasted with the dorsal centers for taste. But if the anterior 

 end of the brain tube lies near the preoptic recess in the lamina 

 terminalis, this difficulty disappears ; for all structures in front 

 of this point must have been developed from the dorsal wall of 

 the brain tube. That is, the secondary fore-brain, including 

 the entire rhinencephalon, is a dorsal structure. 



Our conclusion, then, is that the morphological relations 



