274 
in the minute structure of the olfactory lobe, ganglion, etc. (CAJAL, 
VAN GEHUCHTEN, RETZIUS and others). 
MARSHALL’s paper on the vertebrate olfactory organ, published 
more than twenty years ago, is highly meritorius. He showed, first, 
that in the chick, elasmobranchs, teleosts and amphibia the nerve 
arises a considerable time before the olfactory lobe is formed. He 
further claimed that the olfactory nerve has a dorsal origin, coming 
from the neural crest, and homologized it with other cranial nerves, 
thus anticipating most of the views that have since been expressed 
regarding its origin and nature. 
MARSHALL’s work was done, of course, before embryologists began 
to distinguish between the mode of origin of ganglionic and medullary 
nerve fibres. Since His’ demonstration (1889) of the separateness of 
these two kinds of fibres, as regards their origin, we have been ex- 
pecting full evidence of the peripheral origin of the fibres of the olfac- 
tory nerve. Observations on the source of these fibres have not been 
in agreement. Both Batrour ’74 and MARSHALL ’78 supposed they 
arose from the brain-wall; BEArp ’85, derived them from two sources, 
cerebral and peripheral, His, entirely from peripheral. Houm ’94 and 
HorrMaNn ’96 conclude that it is impossible to determine by obser- 
vation whether the fibres are derived from the brain-wall or the olfac- 
tory epithelium. Disse’s paper (96 and) °971) on “Die erste Ent- 
wickelung des Riechnerven” shows the source of the olfactory fibres 
in the chick, by GoLGı methods, to be from the olfactory epithelium. 
This is one of the most recent and most important contributions to 
our knowledge of the olfactory. 
The knowledge of the minute structure of the lobe has also been 
much extended by CAJAL, VAN GEHUCHTEN, KÖLLIKER, RETZIUS and 
others. 
Meanwhile the early embryonic history of the nerve has not. been 
elucidated, and, even today, we do not possess the complete history 
of this nerve in any one animal. The most conspicuous gap in our 
knowledge is in that section of its history prior to the formation of 
the olfactory lobe, and the question of its nature and relationship to 
the other cranial nerves revolves around this us a pivotal point. 
The fact that the olfactory nerve has a separate existence both 
prior to and after the formation of the lobe has been frequently over- 
looked, and the tractus, a derivative of the lobe, made to usurp its 
1) Anatomische Hefte, Bd. 9, 1897, p. 257—299. Consult this 
paper for references to the Literature. 
