137 



It has been shown by 5diriger ( '9^) that the special pal- 

 llal olfactory coniucting path characteristic of higher verte- 

 brates appear? for the first time in the brain of the reptile. 

 Both "iliin^er ani Herrick have also shown that the first sense 

 to thus enter the field of consciousness is the olfactory one. 

 The palliirn of the selachian really anticipates the reptilian 

 olfactory connection, although, of course, in a much simpler 

 way. In Vmstelus, we therefore find quite a primitive condi- 

 tion represented. 



3o far as we may be permitted to interpret morphological 

 facts, the palltjm of Mustelus would appear to be a long-dis- 

 tance motor centre of the olfactory apparatus. Other olfacto- 

 motor centres there certainly are in abundance. Both the gener- 

 al striatum and the nucleus neuroporicus contribute motor neu- 

 rones to the tractus strio-thalamlcus; while the nucleas post- 

 olfactorius sends a tract to the nucleus habenulae. These 

 centres obtain connection with posterior regions only through 

 relays in both the interbrain and the midbrain. The pallium, 

 on the other hand, sends its tract directly through the base 

 of the interbrain toward the nuclei of the great nerves of the 

 oblongata. The tractus pallii, therefore, gives the olfactory 

 sense an additional hold on the nervous system, a series of 

 connections which cannot obtain, of course, in those fishes 

 with membranous pallia. 



The phylo^enetic development of the pallium of selachians 

 would thus appear to be the outcome of the great dependence 



