the derivation of the adult brain from this primitive state. From the
fore-brain vesicle, a hollow outgrowth on either side gives rises to the
(paired) cerebral hemisphere (c.h.), which is prolonged forward as the
olfactory lobe (o.l.). From the fore-brain the retina of the eye and the
optic nerve also originate as an, at first, hollow outgrowth (op.). The
roof of the mid-brain is also thickened, and bulges up to form two
pairs of thickenings, the corpora quadrigemina, (c.q.). The hind-brain
sends up in front a median outgrowth, which develops lateral wings,
the cerebellum (cbm.), behind which the remainder of the hind-brain is
called the medulla oblongata, and passes without any very definite
demarcation into the spinal cord.