(4.02)

Each cerebral hemisphere contains a cavity, the lateral ventricle, that's filled with cerebrospinal fluid. The lateral ventricle has an anterior horn, a body, a posterior horn, and an inferior horn. The anterior horn is in the frontal lobe, the body is in the parietal lobe, the posterior horn is in the occipital lobe, and the inferior horn curls downward and forward into the temporal lobe.

To see where the lateral ventricle communicates with the third ventricle we'll go round to a medial view. The communication is here, at the interventricular foramen.

To see how the lateral ventricle, the third ventricle, and the fourth ventricle are connected, we'll look at a brain that's been divided in the midline.

Here's a midline section through the third ventricle. Here's the third ventricle. This strand of vascular tissue in the roof of the ventricle is the choroid plexus, which produces cerebrospinal fluid. Here's the interventricular foramen, opening into the lateral ventricle.

The choroid plexus passes through the foramen, and continues into the lateral ventricle. The cerebrospinal fluid that's formed in the lateral and third ventricles passes through this narrow passage, the cerebral aqueduct, and into the fourth ventricle.

Fluid leaves the fourth ventricle through three openings, the lateral apertures (the right one is in the depths of this recess) and the medial aperture, which is in the mid-line here. It's easier to visualize the medial opening in this dissection. Here it is, in the inferior medullary velum. The lateral openings are here.

The medial opening comes out here between the cerebellum and the medulla. The lateral opening on each side comes out just below the cerebellar peduncles.

These openings lead to the subarachnoid space surrounding the brain and spinal cord. We'll see where the cerebrospinal fluid is absorbed later in this tape, when we look at the blood vessels.

We'll return now to the underside of the cerebrum, to look at the structures that form the floor of the third ventricle, which is here. Here's the optic chiasm. Behind it this tubular structure that's been divided, is the infundibulum, the stalk of the pituitary gland. These two projections are the mamillary bodies.

To see how the pituitary gland is attached to the brain we'll look at an intact specimen divided in the midline. Here's the floor of the third ventricle, here's the optic chiasm, here's the infundibulum, leading down to the pituitary gland or hypophysis. The anterior and posterior parts of the pituitary gland are quite distinct.

The pituitary gland sits in the pituitary fossa. The pituitary fossa bulges downwards into the roof of the sphenoid sinus. This area just above the pituitary stalk is the hypothalamus.

In the dissections we've seen so far, including this one, the picture has been simplified by removing the important arteries that surround the base of the brain and run in the major sulci. We'll see these later in this tape.