NEAL: NERVOUS SYSTEM IN SQUALUS ACANTHIAS. 241 
Froriep, in speaking of neuromeres and their nerve relations, said that 
these relations are in no way of such a kind that both nerves and neu- 
romeres appear to be constituent parts of a simple organ system. The 
nerves, especially the trigeminus and facialis, are not so constant in 
their relation to the folds as would be expected, if the latter were 
primary segments of the nervous system. It looks much more as if the 
presence and position of the nerves determines the position of the folds, 
and as if the appearance of the folds is itself a passive, mechanical one, 
necessitated by quick growth in length in a confined space. On the 
basis of his research, he was therefore much inclined to consider these 
late appearing and transitory segments of the brain as morphologically 
unimportant phenomena, 
Broman (’95) has given a somewhat extended description of the fold- 
ings in the hindbrain of a human embryo about three weeks old. Although 
he nowhere formulates his conclusions as to the significance of the folds, 
it is evident that he does not regard them as of phylogenetic significance, 
for he says that the correspondence which earlier investigators have 
found in their relation to nerves seem to him of little help. In his 
opinion the results, differ too much to allow one to think that a general 
rule prevails in the Vertebrate series as regards the number and rela- 
tions of the foldings. The foldings, he says, are intensified in the re- 
gions of the greatest flexure of the neural tube, and in these regions the 
radial arrangements of cells in the foldings is also more marked. This, 
together with the fact that the foldings are confined to the ventral half 
of the medulla, harmonizes well with a mechanical explanation of their 
origin. Upon the evidence that rounded cells (which he thinks are the 
neuroblasts) with round nuclei may be distinguished in the centre of the 
most strongly developed parts of the brain foldings, Broman (’95, p. 189) 
forms an hypothesis concerning the origin of the separation of lateral and 
ventral roots. He says: “Wenn wir noch einmal alle die oben von mir 
als Neuromeren bestimmten Falten durchmustern, finden wir, dass nur 
das als Abducensneuromer bezeichnete die ventrale Wand des Hirnrohres 
ausbaucht. Alle übrigen sind entweder ganz und gar davon abgedrängt, 
oder auf dem Wege es zu werden. Dies kann natürlicher Weise ein 
blosser Zufall bei diesem Embryo sein.” 
Since Broman’s paper is, with the exception of Locy’s, the most recent 
one on the question of neuromeres, I will discuss his evidence and con- 
clusions at some length, It is unfortunate for the purpose of discussion 
that he has failed to identify correctly the cerebellum Anlage. What 
he calls Cerebellumanlage is the posterior of the two secondary sub- 
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