THE CRANIAL NERVES AND LATERAL SENSE ORGANS OF FISHES. 201 



condition, there are several cases on record where on the disappearance of the spiracle the 

 pre-spiracular accompanies for a time the post-spiracular nerve and thus becomes a 

 topographical, but not a morphological, post-spiracular nerve. It seems to me that when 

 the early development of the nerves of Amia has been investigated it will be found that 

 the " internal mandibu.lar " nerve is morphologically pre-sj)iracular, though occupying a 

 post-spiracular position in the adult. This is what we know has happened in Raiia (cp. 

 Strong's " iuternal mandibular "), and what has douljtless also happened in Chliiiceni, and 

 Gadtis. The degeneration of the spiracular cleft naturally leaves the nerves unaffected, 

 since they ai'C concerned rather with the sensory and motor supjDly of the arches, and tli*; 

 latter are untouched by the disaj^pearance of the spiracle. With regard to the second 

 condition above, that is practically i'ulfilled, and so doubtless also is the third. The 

 "internal mandibular " nerve is certainly not a motor nerve in Amia, in which aise it 

 must be a visceral sensory nerve, and indeed AUis says tliat it " is distributed to the inner 

 surface of the liyoid and mandibular arches" (6, p. 745). The "internal mandibular" 

 nerve of Amia therefore is, as far as our knowledge of it goes, a morphological pre- 

 spiracular nerve, and in any case is excluded from l)eing the true internal mandibular 

 nerve, since this should be distributed to the muscles of the hyoid arch, and is undoubtedly 

 represented in Amia by the E-r. hyoideus and opercularis. In further criticism of the 

 passage quoted above I may remark that it is very much " open to question " that the 

 internal mandibular of Amia corresponds to the nerve of the same name described by 

 Ewart. The nerve of the latter author is a motor nerve partly to the muscles of the 

 hyoid arch, and as such differs essentially from the nerve in. Amia. The nerves described 

 b}' Pollard *, Gaupp (1893, 84), and Strong, are correctly homologised, Init should not 

 have been named "internal mandibular," as Miss Piatt (1890, 158, p. 534) and the 

 writer have pointed out. Finally, an anterior brancliial ramus is related to the posterior 

 and not to the anterior face of its arch, as Allis himself mentions is the cise with the 

 " internal mandibular " of Ilcptaiichus. Pinkus (1891, 157) introduces further confusion 

 into the synonymy of the facial nerve of fishes. He correctly homologises his " inferior 

 palatine VII " with the chorda tympani (but did not I'ecognize that this nerve represented 

 the pre-spiracular nerve of other fishes), and divides the morphological post-spiracular 

 nerve ( = , + the lateral line element, the hyomandilnilar trunk) into three parts— 

 (1) internal mandibular ; (2) hyoideus f ; and (3) motor Vllth. Pinkus is of course wrong 

 in using two synonyms (i. e. internal mandibular and hyoideus) to describe two different 

 branches, and it seems to me that 1 and 3 together represent the internal mandibular of 

 other fishes. The motor Vllth branches correspond undoubtedly to the ramus oper- 

 cvilaris facialis of the bony fishes. 



There is hence some confusion in the terminology of the facial nerve of fishes, which it 

 is desira])le should be removed. I have therefore drawn up a scheme of the constitution 

 of the facial or Vllth cranial nerve in a typical fish, with the synonyms of the three 

 cardinal branches. It is to be hoped that future authors will, before naming a nerve, 

 first ascertain whether it is somatic or splanchnic, and then whether it is sensory or 



■^ * See 1S92. 160, pp. '.VJl and :i9b (table). It will fie seen that Pollard's nerve is the one I have id(>ntified as 

 the chorda tympani in Gadtis. 



f As this is a sensory nerve it must he unrepresented in other fishes. 



