264 THE DEVELOPMENT OF THE CHICK 
from the central ends of the neuroblasts and grow into the 
mesenchyme towards the fore-brain. At the same time groups 
of epithelial cells free themselves from the inner face of the 
olfactory epithelium, and come to lie between this and the fore- 
brain. The axones of the neuroblasts grow between these cells 
until they reach the base of the fore-brain over which they spread 
out, entering the olfactory lobe about the sixth day (Figs. 155 
and 156). In the meantime the peripheral ends of the olfactory 
neuroblasts have extended out as broad protoplasmic processes 
to the surface of the olfactory epithelium, and thus form the per- 
cipient part of the olfactory sense-cells. 
Iria. 155. — Olfactory epithelium of a chick embryo of 5 
days, prepared by the method of Golgi. (After Disse.) 
a, b, and e indicate different forms of neuroblasts in the 
olfactory epithelium. 
The epithelial cells between fore-brain and olfactory pit, through 
which the axones of the olfactory neuroblasts grow, are for the 
most part supporting and sheath-cells of the nerve, but they in- 
clude a few bipolar neuroblasts (ig. 156). The latter are to 
be considered as olfactory neuroblasts with elongated protoplas- 
mic processes. 
Rubaschkin finds a ganglion, which he ealls ganglion olfactortum 
nervi trigemini, situated beneath the olfactory epithelium in a nine- 
day chick. The bipolar cells send out processes peripherally which end 
in fine branches between the cells of the olfactory mucous membrane, 
and centrally, which go by way of the ramus olfactorius nervi 
trigemini towards the Gasserian ganglion. 
2. The Second Cranial or Optic Nerve. The course of this 
