affairs in the adult. The brain is seen in median vertical section. (ch.)
is the right cerebral hemisphere, an inflated vesicle, which, in the
mammal-- but not in our lower types-- reaches back over the rest of
the fore-brain, and also over the mid-brain, and hides these and the
pineal gland in the dorsal view of the brain (Figure 2). The hollow of the
hemisphere on either side communicates with the third ventricle, the
original cavity of the fore-brain (1 in Figure 5), by an aperture (the
foramen of Monro), indicated by a black arrow (f.M.). Besides their
original communication through the intermediation of the fore-brain,
the hemispheres are also united above its roof by a broad bridge of
fibre, the corpus callosum (c.c.), which is distinctive of the
mammalian animals. The original fore-brain vesicle has its lateral
walls thickened to form the optic thalami (o.th.), between which a
middle commissure, (m.c.), absent in lower types, stretches like a
great beam across the third ventricle. The original fore-brain is often
called the thalamencephalon, the hemisphere, the prosencephalon,
the olfactory lobes, the rhinencephalon.