256 Journal of Comparative Neurology and Psychology. 



is to be noticed between this and the decussation between the 

 secondary vagus nuclei in the cerebellum. Decussating fibers 

 of the second and third order are present in each case. A 

 further point of comparison is found in the fact that the ganglia 

 habenulae appear to be a part of the central grey some distance 

 removed from the dorsal wall of the brain, which here is a 

 choroid plexus. If we accept the supposition that the somatic 

 sensory nucleus of the diencephalon has degenerated, the 

 morphological position of the ganglia habenulae corresponds 

 rather closely to that of the secondary vagus nucleus beneath 

 the somatic sensory centers of the cerebellum. The choroid 

 plexus of the diencephalon is regarded as morphologically 

 equivalent to the optic lobes or dorsal part of the cerebellum 

 and the ganglia habenulae are morphologically lateral. These 

 hypotheses have a significance in connection with the question 

 of the relation of the olfactory and gustatory organs and centers 

 discussed above. 



Not enough is known about the epiphysial decussation to 

 admit of any discussion. 



The anterior commissure consists of two distinct parts: a 

 smaller, anterior portion, sometimes isolated, composed of fibers 

 from cells of the olfactory bulb destined to the epistriatum ; and 

 a larger portion composed of fibers from the inferior lobes also 

 destined to the epistriatum. A third element, consisting of 

 fibers from the lateral cortex to the opposite epistriatum, need 

 not be considered since it is not primitive in vertebrates. The 

 tract from the inferior lobes is a tertiary tract which may be 

 either olfactory or somatic sensory in character. We have seen 

 reasons for thinking that the hypothalamus has been modified by 

 the entrance into it of the somatic sensory tracts. We must 

 therefore regard the secondary (and tertiary?) olfactory tracts as 

 constituting the primitive portion of the anterior commissure. 

 The writer is unable to see any resemblance between this and 

 the somatic sensory decussation, while there is a certain simi- 

 larity between the anterior commissure and the splanchnic sen- 

 sory decussations of the ganglia habenulae and the secondary 

 vagus nuclei. If the anterior commissure is to be compared 



