Ruptured saccular aneurysm; junction of internal carotid and posterior communicating arteries: This is a close-up view of the chiasmal region on the inferior surface of the cerebral hemispheres. The basilar artery and brain stem lie in the lower part of the picture with the frontal region above. The cut ends of the optic nerves are in the central portion of the upper edge of the slide, adjacent to the cut stems of the internal carotid arteries. On the right side of the slide there is an out-pouching which arises from the internal carotid artery at the site of origin of the posterior communicating artery. (Compare with opposite side). This is a saccular aneurysm that has ruptured, causing extensive hemorrhage into the subarachnoid space.