io8 Bulletin of Laboratories of Denison Utiieivsity. [Voi. xiii 



a similar derivative of the substantia reticularis <^risea. The 

 lemniscus (fasciculus lateralis) of these fishes represents a simi- 

 lar specialized somatic sensory path from the primary tactile 

 and acustico-lateral centers to the nucleus lateralis mesencephali 

 (torus semicircularis, or colliculus), whose fibers cross in the 

 ventral commissure of the oblongata. This special splanchnic 

 (gustatory) path appears to have been differentiated later in the 

 phylogeny than the secondary somatic path. Hence its super- 

 ficial position, coenogenetic structures of the brain being gen- 

 erally added external to palingenetic structures. The crossing 

 of the visceral path within its terminal nucleus instead of at its 

 origin in the oblongata is perhaps due to the same cause, the 

 primitive undifferentiated visceral path having been uncrossed or 

 diffusely crossed because these sensations are not localized ordi- 

 narily. The?/«.f/><f67'rt//^r(^secondary visceral path doubtless is as 

 primitive as the unspecialized somatic path and probably was 

 originally a diffuse connection by short fibers in the substantia 

 reticularis (crossed or uncrossed). But the ascending gustatory 

 tract (specialized visceral) as a well defined conduction path is 

 quite certainly more recent. This does not affect the conclu- 

 sion to which we were led above that the visceral root fibers 

 (fasciculus communis) are older than the special somatic centers 

 in the tuberculum acusticum. 



The topography of the oblongata suggests that upon the 

 ■ basis of the unspecialized centers the ascending secondary 

 paths for the specialized systems were added in the following 

 order, — first, the somatic sensory, or lateralis system for orien- 

 tation and equilibrium, and, second, the gustatory. The latter 

 is a strictly visceral system except that in some fishes impor- 

 tant somatic secondary connections appear sporadically in cor- 

 relation with the appearance of taste buds in the outer skin. 



The mammalian homologies of the superior secondary gus- 

 tatory nucleus cannot be determined until its relations to neigh- 

 boring structures are much more fully known. Stieda's origin- 

 al designation, "Uebergangsganglion," apparently included 

 much more than the secondary gustatory center, which is prob- 

 ably coextensive with Maysek's narrower term, "Rindenknot- 



