The effectiveness of cerebral angiography is considerably enhanced by selective catheterization of the external carotid artery. The advantages are as follows: 1. The procedure permits differentiation of extrinsic from intrinsic cerebral tumors and is of value in supratentorial as well as infratentorial masses (Figs. 1 and 2). Characteristically, meningiomas have a double blood supply: the external carotid artery supplies the central portion of the tumor, and the internal carotid artery the periphery (Fig. 3). In many instances meningiomas are also nourished by the superficial temporal or the occipital arteries. Not all extracerebral masses are meningiomas, however, nor are all meningiomas supplied by the external carotid artery. Intrinsic tumors invading the dura may derive blood from the middle meningeal artery, but not other branches of the external carotid artery. Negative findings may be of value (Fig. 4). 2. Failure to demonstrate the external carotid circulation may result in a tumor being thought...