THE CRANIAL NERVES AND LATERAL SENSE ORGANS OF FISHES. 199 



T. Special Considerations. 



Schulze (1870, 182) was the first author to state that the lateral canals arose in 

 sections with a sense organ in each section, and that the dorsal tubules were formed by the 

 fusion of the adjacent extremities to form a single peripheral tubule and pore. This was 

 confirmed by Solger (1880, 193), Bodeustein (1882, 24), and AUis (1889, 4) — the latter's 

 work in tliis connection having been previously referred to. Friant (1879, 73) indepen- 

 dently discovered with Schwalbe that tlicre were two siqjerficial oplithalmic nerves, and 

 further has the credit of being the first author to approximately arrive at a correct 

 appreciation of the trigeminal and facial nerves of fishes, being the first writer to hold 

 that the superficial ophthalmic and l)uccal lateral line nerves were not branches of the 

 trigeminus*. He says (p. 103): — "Le nerf facial nait isolement des cotes du bulbe, 

 au-dessus de la racine posterieure du trijumeau, se distribue aux meninges, a la peau et 

 aux canaux muqueux du sommet de la tete et de la region sous-orbitaire, aux teguments 

 d'enveloppe de Freil et de I'orifice nasal, a la peau et aux teguments fibro-musculaires 

 du museau, aux muscles peaueiers de la joue, et chez la Perclie, a la jieau de la reo-ion 

 dorsale et aux muscles des nageoires dorsales." It will lie seen that for the time it was 

 written this was a very accurate description, and its historic imjjortance makes it 

 extraordinary that Friant's work should hitherto have been overlooked. 



The fishes are classified by Sappey (1880, 175) into four groups according to the 

 development of tlie lateral line system : — (1) the Plagiostoma, in which it is greatest 

 developed ; (2) " L'Ange et les Squales," not so well marked ; (3) the majority of the 

 bony fishes, where it is more reduced than in 2 ; (1) fishes having no lateral line system 

 at all[!]. Such a classification, based on so very variable a structure (even though its 

 general anatomy is identical in nearly all fishes), is necessarily artificial, and has little or 

 no taxononiic value. It ^^■ould involve, for example, placing Jmia alongside Gadus. 

 Baudelot (1883, 16) states that the facial nerve is absent in many bony fishes {e.g. the 

 " Cariae ") and that in these forms it is represented by a branch of the trigeminus. Such 

 a statement must be due to imperfect observation, and if by " Carpe " we may under- 

 stand Cyprinus, a true facial nerve was described by several authors in that form long 

 before the time at which Baudelot was writing. 



Sagemehl (1881, 172) emphasizes the fact that the two dorsal lateral canal commissures 

 are not homologous, and that a parietal commissure cannot be considered to represent 

 a supra-temporal commissure where in any genus the former is the only one found. 

 Eamsay Wright (1885, 229) considers (p. 491) that in Lepidosteiis a portion of the 

 R. oticus facialis represents the prsse-trematic or prge-s2)iracular branch of the facial, 

 since it supj)lies the anterior sense organ of the spiracular cleft, and states that a similar 

 condition is found in Amia. It is impossible that the two nerves mentioned can be 

 homologous, since the otic is a true lateral line nerve and cannot, therefore, be compared 

 with a nerve consisting of visceral sensory fibres. Wright, therefore, failed to find a 

 prae-spiracular nerve in Lepidosteus and Amia. 



* Confirmed independently in 1881 by Marshall and Spencer, and in 1889 by Allis (4, pp. 513, 514). 



