248 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
cessive nerves, the facialis and the glossopharyngeus, to two successive 
encephalomeres (V and VI), seems to me to be a very important fact. 
The cells of the glossopharyngeus are crowded back by the ear capsule, 
but the fact that in their ventral course they are directed anteriorly into 
the third visceral arch goes to prove that their posterior position is not 
their primitive one. Almost as clear is the relation of the cells prolifer- 
ated from encephalomere VII to the second branchial (4th visceral) arch. 
From these facts I was led to think that the primitive relations of the 
hindbrain neuromeres were with the visceral arches. The fact that the 
hindbrain neuromeres are local thickenings of the lateral walls of the mer 
dulla also leads to the opinion that they are segmental groupings of the 
“Kerne”? of the nerves of the visceral arches. With this hypothesis in 
mind, I have examined the evidence in S. acanthias, as well as in other 
forms, in order to see if the facts support it, The more primitive rela- 
tions would be expected to occur in S. acanthias. From encephalomere III 
are proliferated neural-crest cells which enter the mandibular arch ; later 
this encephalomere becomes related with the motor root which innervates 
the muscles of this (mandibular) arch. Its relations, then, are clearly 
with the first visceral arch, and we may therefore assume that its local 
“nucleus” of the trigeminus. 
thickening contains, at least in part, the 
The evidence obtained from the study of the relations of encephalo- 
mere IV seems at first sight strongly against the hypothesis. Few cells 
are proliferated from this neuromere. Late in its development the fibres 
of the sensor root of the trigeminus connect with its convexity. It 
forms a marked exception in its nerve relations to the other hindbrain 
neuromeres. Were it not that other facts are found which serve to bring 
this apparent exception into harmony with the hypothesis, the adverse 
evidence it presents would scem an insurmountable obstacle to the 
acceptance of my view. Neural-crest cells which pass into the second 
visceral (the hyoid) arch are proliferated from hindbrain neuromere V, 
and the motor fibres in relation with this neuromere innervate the mus- 
cles of this arch, From hindbrain neuromere VI are proliferated: the 
neural-crest cells which pass into the third visceral (1st branchial) arch, 
and the motor fibres of the glossopharyngeus, of which these cells form 
the ganglionic Anlage, innervate its musculature. The place of origin 
of the fibres of the glossopharyngeus is crowded backward, evidently by 
1 Hoffmann (94) has spoken of the paired segmental outpocketings of the 
neural tube of this region. 
2 That is, they may be localizations of the motor “ Kerne” and of the sensor 
“ Endkerne” of the nerves primitively related to them. 
