l66 NERVE COMPONENTS OF BONY FISHES. 



chorda tympani. The r. pre-trematicus in the strict sense 

 (number i of Stannius' description) may have fused with 

 this nerve, or more likely has disappeared with its demi- 

 branch. Midway of its course it receives an anastomosing 

 branch from the facial proper (post-spiracular) and this is 

 probably the post-trematic communis element of the facial, 

 secondarily and incompletely joined to the pre-trematic 

 ramus — a conclusion suggested to me by Mr. Cole in 

 private correspondence. 



An anastomosis of the type presented in Chimaera is 

 unusual. More often it is the r. pre-trematicus and 

 chorda which lose their identity after the closure of the 

 spiracle, either by fusion with the post-trematic facial 

 ("facial proper " of Ewart and Cole) or by fusion with 

 the post-trematic trigeminus (r. mandibularis V). The 

 latter type is the one which would most naturally occur, 

 since both of the anastomosing nerves run along the same 

 arch; and, in fact, it is apparently most frequently found 

 among the fishes. It does not, however, appear in 

 Menidia; for this fish, as we shall see beyond, lacks com- 

 munis fibres in the r. mandibularis V, though such fibres 

 occur in the r. maxillaris. But Menidia does possess a 

 distinct nerve (to be described in the next sub-section) 

 between the truncus hyomandibularis and the trigeminus 

 which distributes to the region of the pseudobranch and 

 which I regard as the r. pre-trematicus VII (in the narrow 

 sense). 



In Amia, Allis finds communis fibres in both the max- 

 illary and the mandibular rami of the trigeminus. These 

 fibres come ' ' from the ganglion of the fasciculus com- 

 munis root " ('95, p. 488), i. e., the geniculate ganglion, as 

 in Menidia. Since there are no communis (z. e., pre-spi- 

 racular VII) fibres in the r. mandibularis V in Menidia, 



