131 



The Truncus hyomandibularis {t. km.) 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 - 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 Yii. (y^05^. 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 demibVanch, 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 hyomaudibular 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. 



■f 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). 



