Now we'll move on to look at the cerebrum. Here's the cerebrum with the brainstem attached and the cerebellum removed.
The functions of the cerebrum include the senses of vision, hearing, smell, touch and spatial perception, and also speech and language, memory, thought and voluntary action. The cerebrum is formed mainly by the two cerebral hemispheres. These are separated in the midline by the falx, which occupies this longitudinal cerebral fissure.
Though they look hemispherical from in front, the shape of each cerebral hemisphere is more complex when seen from the side. In front this part, the frontal lobe, occupies the anterior cranial fossa. This part below, the temporal lobe, occupies the middle cranial fossa. This part behind, the occipital lobe, lies above the tentorium.
The two cerebral hemispheres are connected across the midline by the corpus callosum, which runs all the way from here in front, to here behind. The two cerebral hemispheres are connected below by the two cerebral peduncles converging on the brainstem. They're also connected by the structures of this area, the floor of the third ventricle.
To see these connecting structures better we'll look at a brain that's been divided in the mid-line. Here's the corpus callosum. This is the cerebral peduncle.
The third ventricle is here. Here's the third ventricle in the model: it's quite narrow from side to side. This is the floor of the third ventricle.
The surface of each cerebral hemisphere is richly folded. Each inward fold, or sulcus, and each outward fold, or gyrus, has a name, but here we'll name only two, the central and the lateral sulci.
This is the lateral sulcus. It's very deep. It extends all the way round to here on the underside. Here's the medial end of the lateral sulcus in the intact brain. The lateral sulcus separates the frontal lobe above from the temporal lobe below.
This long sulcus running upwards and backwards is the central sulcus. It's the only one that runs all the way to the medial surface of the hemisphere.
The cerebral hemisphere is described as consisting of four lobes, the frontal, temporal, and occipital lobes that we've mentioned already, and the parietal lobe. Between the frontal lobe and its neighbors the central and lateral sulci form natural boundaries. The other boundaries are somewhat arbitrary.
Here are the four lobes on the medial surface: frontal, parietal, occipital, and temporal. The sloping underside of the occipital lobe conforms to the upward slope of the tentorium.
Here are the two temporal lobes seen from below. This part of the tip of the temporal lobe is the uncus. The uncus lies just above the tentorial incisure, which is here.
Here on the underside of the frontal lobe is the olfactory tract. It ends in the olfactory bulb, from which the fibers of the first cranial nerve, the olfactory nerve, emerge.