FIG. 9.—Diagrammatic side view of brain, showing cerebellum (CB) and medulla oblongata
(MO). F' F'' F''' are placed on the first, second, and third frontal convolutions, respectively; AF,
on the ascending frontal; AP, on the ascending parietal; M, on the marginal; A, on the angular.
T' T'' T''' are placed on the first, second, and third temporal convolutions. R-R marks the fissure
of Rolando; S-S, the fissure of Sylvius; PO, the parieto-occipital fissure.The surface of each hemisphere may be thought of as mapped out into four
lobes: The frontal lobe, which includes the front part of the hemisphere and
extends back to the fissure of Rolando and down to the fissure of Sylvius; the
parietal lobe, which lies back of the fissure of Rolando and above that of Sylvius
and extends back to the occipital lobe; the occipital lobe, which includes the
extreme rear portion of the hemisphere; and the temporal lobe, which lies below
the fissure of Sylvius and extends back to the occipital lobe.
The Cortex.—The gray matter of the hemispheres, unlike that of the cord, lies
on the surface. This gray exterior portion of the cerebrum is called the cortex,
and varies from one-twelfth to one-eighth of an inch in thickness. The cortex is
the seat of all consciousness and of the control of voluntary movement.