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While this nerve has a sensory moiety, some facts have been 

 brought forward which suggest that it has also, possibly, a motor 

 moiety. There are two roots, and in the skate, both niedullated and 

 non-medullated fibres have been observed in this nerve. 



It will be extremely difficult to determine its physiological pro- 

 perties by experimentation. Its minuteness will render any mani- 

 pulation or experimental study difficult without giving injury to the 

 olfactory. 



This new nerve must not be confused with the thalamic nerve 

 discovered in 1891 by Platt and Frokiep, and whose history was 

 so well worked out by Hoffmann in 1897. The thalamic nerve is 

 between the mid-brain and the thalamencephalon. The new nerve 

 and the thalamic exist simultaneously in embryos of Squalus acanthias, 

 but the latter is transitory. 



Neither , in my opinion , is it related to the Trigeminus. Its 

 individual character is so well marked that there is nothing to bear 

 out the idea that it has escaped from the territory of the Trigeminus ; 

 rather, it bears the marks of an ancient nerve, whose physiological 

 importance has become reduced by the more rapid development of 

 other nerves. 



It is doubtful if any trace of it be preserved in higher verte- 

 brates. Whatever its original function may have been , it was in 

 some way superceded in the evolution of animal life, and having 

 first lost its importance, it thereafter disappeared. I have looked 

 with especial care for it in a number of amphibians and teleosts, and 

 in the chick. Both embryonic and adult stages have been examined 

 in Necturus, Amblystoma, the frog, the toad, the trout, the catfish and 

 the chick, but in none of them has the nerve been found. 



From any point of view, it is extremely interesting, that we have 

 preserved so fully in Selachians and Dipnoi, a ganglionated nerve in 

 front of the optic, bearing in its anatomy testimony as to its ancient 

 features, but of which all traces have disappeared in higher animals. 



If the view as to its nature which I have expressed be true, the 

 story of the development and present condition of this nerve furnishes 

 a little footnote to the ancestral history of the vertebrate brain. 



