ORGANS OF SPECIAL SENSE 283 
The Optic Nerve. Owing to the relations established by the 
choroid fissure, the floor of the optic stalk is continuous from the 
first with the inner layer of the retina (Fig. 96 B), and it furnishes 
the path along which the optic nerve grows. The axones of the 
optic nerve originate, for the most part, from the retinal neuro- 
blasts, composing the layer next to the cavity of the optic cup, 
and their growth is thus centripetal. They are first formed in 
the fundus part of the retina, and grow in the direction of the 
Fic. 163. — Outlines of sections in the planes a, b, ¢, e, of 
Fig. 163. (After Bernd.) 
bl. v., Blood vessel. i. 1., Inner or retinal layer of the 
optic cup. o.1., Outer or pigment layer of the optie cup. 
P. inv., Angle of invagination of the pecten. Other ab- 
breviations as before. (Fig. 162.) 
optic stalk between the internal limiting membrane and the neu- 
roblast layer (ganglion cell layer), thus forming a superficial layer 
of axones; their formation begins on the fourth day, and there is 
a period about the end of this day when axones are found in the 
distal part of the optic stalk, next to the bulbus oculi, but not 
in the proximal part, next to the brain. This observation affords 
conclusive proof of the retinal origin of the fibers of the optic 
