188 EDWARD PHELPS ALLTS, JUN. 



backward over the columella and then gives off its ramus 

 mandibularis internus^ which Graupp considers the un- 

 questioned homologue of the chorda, " der ohne jede weitere 

 Beziehung zur Ohrcolumella aussen um das Zungenbeinhorn 

 herum zu seinem Endgebiete am Unterkiefer verlauft." In 

 Eeptilia^ on the contrary, the mandibularis internus is said to 

 take a recurrent course and to pass forward over the columella 

 again to reach its destination, thus having exactly the oppo- 

 site relations to that structure that it is said to have in 

 Amphibia. 



While I am unable to even properly follow this discussion, 

 in so far as it relates to mammals, it is evident that Dixon's 

 figure 15 shows a striking resemblance to the conditions found 

 in Amia, the chorda tympani being considered as postspiracu- 

 lar in position, and as represented in the mandibularis 

 internus facialis of the fish, and the mandibularis internus 

 trigemini of Amia being considered as the homologue of the 

 lingual nerve of man. It is of course possible that the 

 mandibularis internus trigemini of Amia may contain both 

 facial and trigeminal fibres, and hence represent not only the 

 lingual nerve but also the chorda, if that nerve be a pre- 

 spiracular one. 



In short, if the chorda be a prespiracular nerve I look for 

 its homologue in the mandibularis internus trigemini of my 

 descriptions of Amia. If it is a postspiracular nerve it must 

 be represented in the mandibularis internus facialis of the 

 same fish. 



In this connection it seems projDer to give quite fully the 

 late Prof. Huxley's opinion of this nerve, as set forth in the 

 unpublished manuscript to which I have already made 

 reference. In this memoir Prof, Huxley first describes the 

 chorda in man as a branch of the posterior division of the 

 portio dura or seventh nerve. He then says that, " In the 

 frog, the portio dura arises in close connection with the 

 aviditory nerve from the medulla oblongata, and as it passes 

 outwards becomes so intimately united with the Gasserian 

 e-anfflion that it has been commonly described as a root of the 



