131 
The Truncus hyomandibularis (¢. 4m.) is formed by 
the union of three nerve bundles as described above. It 
contains the following four components as in Menidia, but 
the second is absent in Gadus :— 
1. Cutaneous - - - Ni 
2. Communis 
3. Lateral line ventral root ' VII. 
4. Motor 
Just as the Truncus leaves the jugular foramen it 
gives off a communis nerve which we have identified as 
the 
7. Post-trematicus vii. (os¢. vi7.)—This nerve after 
a short course through 10 sections fuses with the very 
large communis nerve from the glossopharyngeus known 
as Jacobson’s anastomosis (Jac. anast.).* The  post- 
trematicus vil. arises considerably ventral to and quite 
separately from the palatinus vii. Judging from its blood 
vessels and innervation we regard the pseudobranch of the 
Plaice as a single Ayotdean demibranch, but whether 
anterior or posterior we have not been able to determine. 
In this we differ from Herrick,t who regards the pseudo- 
branch of Menidia as a mandibular demibranch, and hence 
our post-trematicus vii = his pre-trematicus vii. We 
have, however, no space for a discussion of this question, 
and further it may be, as Herrick suggests, that the 
pseudobranch is not homologous throughout the Teleostean 
series. One of us has formerly maintained that Jacob- 
son’s anastomosis is really the palatinus (pharyngeus) ix. 
*The post-trematicus arises from the hyomandibular trunk directly 
the latter issues from the jugular foramen. Stannius found it in the 
Plaice, and regards it as-a sympathetic nerve, but this of course is an 
error, as the sympathetic is otherwise accounted for. 
t Herrick also states that Jacobson’s anastomosis of Gadus passes from 
vii. toix. It is really of course the other way about, as we state above. 
See a more recent paper by Herrick (Jour. Comp, Neurol. xi., p. 194), 
