534: JULIA B. PLATT. 
which contradicts the evidence given by Gegenbaur (15) for 
viewing the hyoid as equivalent to a single visceral arch. 
To the two possibilities thus suggested by v. Wijhe the 
embryology of Necturus adds a third, for the hyoideus appears 
in Necturus, not as a post-trematic nerve, but as a lateral 
branch of the hyomandibularis similar to those supplying the 
external gills and lateral walls of the following arches. The 
true post-trematic nerve of the hyoid arch is the hyomandibu- 
laris and its ventral continuation, the “internal mandibular.” 
Nor do I regard the external mandibular nerve as the pretre- 
matic nerve of the group, but because of its relation to the 
mouth would homologise it also with the post-trematic nerves, 
the mouth being in my opinion (81) formed by the fusion of 
the ventral parts of one or more pairs of gill clefts. The 
missing cleft in which, like v. Wijhe, I also believe is there- 
fore to be sought in the mandibular arch rather than the 
hyoid—a view that is supported by the endodermic origin of 
the cells forming the mandibular musculature in Necturus 
(32), and by v. Kupffer’s (24) discovery that the cavity which 
gives rise to the mandibular muscles in Petromyzon is in fact 
a pocket of the alimentary canal. 
Of the homologies of the “ chorda tympani” I know nothing, 
but was much surprised to find that Strong, in agreement with 
Pollard (88), affirms that the nerve is represented by the ramus 
mandibularis internus, adding that Froriep (12) may possibly 
have “had the correct nerve, but was mistaken in assigning it 
to the lateral line system” (p. 187). A letter from Dr. Strong 
makes it probable, however, that the branch he designates 
mandibularis internus corresponds to the branch I have called 
“external palatine.’ This nerve is not a branch of the 
hyomandibularis in Necturus, and is certainly not the homo- 
logue of the nerve Froriep calls the external mandibular. 
Hence the confusion. 
8. Cell and Fibre. 
In regard to the formation of the nerves, much that v. 
Kupffer (22, 28) affirms for Petromyzon, and Dohrn (6, 8) for 
