4i6 Journal of Comparative Neurology. 



muscles of expression are derived from the proper mus- 

 culature of the facialis segment. 



It must be left to future embryological studies to deter- 

 mine which of these modes of encroachment has been fol- 

 lowed by the communis nerves which emerge with the 

 VII, IX and X nerves and spread out over the surface of 

 the body. And in the case of the nerves which run for- 

 ward from the V, VII and IX segments into the jaws and 

 facial regions the problem is much more difficult. If the 

 pre-trigeminal nerves ever did conform to the primitive 

 branchiomeric type, this conformity has been so modified 

 in all existing vertebrates as to be unrecognizable. The 

 embryological evidence of pre-oral branchiomeres certainly 

 needs confirmation and the persistence and metameric 

 constancy of the somatic musculature in these segments 

 would tend to separate them farther from the typical 

 branchiomeres of higher forms, at least. The sensory 

 components of these pre-oral segments, with the probable 

 exception of the profundus, seem to have been wholly 

 consumed in the nerves of special sense or to have de- 

 generated altogether. The general sensory functions of 

 these segments must, then, be supplied from the segments 

 farther back, and we should not say that these general 

 sensory nerves of the first segments have been supplanted 

 by those of the following ones, but that the latter have 

 pushed forward because of the atrophy of the proper in- 

 nervation of the first segments. 



Mention should be made in this connection of the sup- 

 posed "vicarious relation" between the V and VII 

 nerves developed by Pinkus ('94) from a study of the re- 

 lations in the Amphibia. He calls attention to the fact 

 that in the aquatic Amphibia the lateralis branches of the 

 VII are highly developed and that these branches assume 



