Fig. 43-10. Computerized axial tomograms of the head, showing the ventricular system as seen in horizontal sections. A and B are from the same subject. A shows the body and posterior horn of each lateral ventricle. The median white line indicates the falx cerebri. The following structures are visible in B, from front to back: the anterior horns curved around the head of each caudate nucleus; the interventricular foramina, barely visible between the anterior horns and the third ventricle, which appears as a median slit; a calcified pineal body, seen as a white dot immediately posterior to the third ventricle; and a transverse, crescentic area behind this, which is the subarachnoid space behind the tectum of the midbrain. In C, the lesser wings of the sphenoid bone and the petrous portions of the temporal bones delimit the cranial fossae. The dorsum sellae appears as a white band between the shadows of the temporal lobes. Between the cerebellar hemispheres, the fourth ventricle is visible as a dark, inverted U. (Courtesy of Giovanni Di Chiro, M.D., Bethesda, Maryland.) In D, the approximate planes of section are indicated. XY, the orbitomeatal plane. Click for high resolution image.