281 
are mainly distributed to the lateral portion of the olfactory cup; a 
large part of them enter into a sort of median keel, which traverses the 
nasal membrane somewhat like the mid-rib of a leaf, proceeding along 
this structure they give off branches right and left which are distri- 
buted to the olfactory 
epithelium. The fibres KS 
from (b) are distri- PE ae 
buted to the median 
half of the cup. The 
condition in the adult 
is the result of se- 
condary modifications 
of the structures now 
existing. The lobe be- 
comes modified into 
bulbus and tractus but 
there is no justifica- 
tion in regarding the 
latter as the nerve, 
even after it becomes 
long and slender, for, 
the olfactory nerve 
consists of the fila 
olfactoria and is a 
true cranial nerve that 
makes its appearance 
long before the lobe. Fig. 7. X. about 101/, diameters. 
When the lobe elon- 
gates it forms a kind of stalk upon the distal extremity of which is 
borne the true olfactory nerve. 
Fig. 8 represents the brain of an embryo 150 mm long about to 
be freed from the oviduct. The lobe (Zob) is much enlarged and the 
olfactory cups are directed forwards. The median nerve (nv) is broken 
on the left side but is entire on the right. Its central connection 
with the brain-wall, as determined by external study, is at the bottom 
of the furrow which partly separates the fore-brain into hemispheres. 
Its path in the furrow is a little more dorsal than ventral and it 
penetrates the brain-wall on the mesial surface of the hemisphere 
very near the point where the two halves are joined. The fibres can 
be traced as united bundles for some distance into the brain tissue, 
I have been unable to determine the precise nature of their central 
