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The lobes of the cerebral hemispheres (fig. 11.16) are named after the skull bones that they underlie. They include the following:

1. Frontal lobe. The frontal lobe forms the anterior portion of each cerebral hemisphere. It is bordered posteriorly by a central sulcus (fissure of Rolando), which passes out from the longitudinal fissure at a right angle, and inferiorly by a lateral sulcus (fissure of Sylvius), which exits the undersurface of the brain along its sides.

2. Parietal lobe. The parietal lobe is posterior to the frontal lobe and is separated from it by the central sulcus.

3. Temporal lobe. The temporal lobe lies inferior to the frontal and parietal lobes and is separated from them by the lateral sulcus.

4. Occipital lobe. The occipital lobe forms the posterior portion of each cerebral hemisphere and is separated from the cerebellum by a shelflike extension of dura mater called the tentorium cerebelli. The occipital lobe and the parietal and temporal lobes have no distinct boundary.

5. Insula. The insula (island of Reil) is located deep within the lateral fissure and is so named because it is covered by parts of the frontal, parietal, and temporal lobes. A circular sulcus separates it from them.

A thin layer of gray matter (2 to 5 millimeters thick) called the cerebral cortex (ser'e-bral kor'teks) constitutes the outermost portion of the cerebrum. It covers the convolutions, dipping into the sulci and fissures. The cerebral cortex contains nearly 75% of all the neuron cell bodies in the nervous system.

Parietal lobe

Central sulcus

Occipital lobe

Transverse fissure

Central sulcus

Parietal lobe

Occipital lobe

Transverse fissure

Central sulcus

Blood Vessels The Gallbladder

Frontal lobe

Longitudinal fissure

Parietal lobe

Occipital lobe

Retracted temporal lobe

Occipital lobe

Figure

Colors in this figure distinguish the lobes of the cerebral hemispheres. (a) Lateral view of the right hemisphere. (b) Hemispheres viewed from above. (c) Lateral view of the right hemisphere with the insula exposed.

Frontal lobe

Central sulcus

Longitudinal fissure

Parietal lobe

Occipital lobe

Retracted temporal lobe

Occipital lobe

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