Immediately above and parallel to the superior edge of the caudate nucleus is a bundle of nerve fibers which has been a bone of contention among neurologists for the last fifty years. In the fixed human cerebrum this fiber bundle may be distinctly seen projecting into the body of the lateral ventricle for about 1 mm. It lies close to the undersurface of the corpus callosum, between it and the head and the body of the caudate nucleus. Covered with the ependyma, it has a glistening white appearance in the fixed brain and is tough to the touch. Its thickness from above downward is difficult to estimate for reasons which will appear later; it is, roughly, about 2 mm. thick. Its width is about one-half that of the internal capsule. Its length, from before backward, as it is seen in the body of the ventricle with the ependyma intact, is