SEA-FISHERIES LABORATORY. 275 



The Truncus hyomandibularis (t. hm.) 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 V. 



2. Communis \ 



3. Lateral line ventral root L VII. 



4. Motor j 



Just as the Truncus leaves the jugular foramen it 

 gives off a communis nerve which we have identified as 

 the 



7. Post-trematicus vii. (post. vii.). — 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 vii. 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 hyoidean 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. 



+ Herrick also states that Jacobson's anastomosis of Gadus passes from 

 vii. to ix. 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). 



