The Internal Basal Ganglia

THE INTERNAL BASAL GANGLIA :—The internal basal ganglia rest upon and are attached to the internal surface of the internal capsule. They are separated from each other by a depression, and a narrow band of white fibres, the tamia semicircularis. The superior internal ganglion, or caudate nucleus, rests upon the upper portion of the internal surface of the internal capsule, and projects into the floor of the lat eral ventricle. Its anterior portion, or body, is large, and occupies the anterior corms of the lateral ventricle. The pos terior part or tail of the caudate nucleus gradually tapers from the body iu front to form a narrow elevation which runs along the outer margin of the lateral ventricle, and, bending beneath the germ of the internal capsule, enters the roof of the middle corm', at the end of which it terminates in a bulbous extremity.

The tamia semicircularis is a narrow band of white fibres at the bottom of a depression which separates the caudate nucleus from the thalamus opticus. It extends along the

whole length of the lower margin of the caudate nucleus. Beginning in front immediately anterior to the anterior pillars of the fornix as a broad surface, it extends backward as a narrow baud which terminates below at the end of the middle cornu and is attached to the apex of the magual convolution.

The tenia semicircularis in the floor of the lateral ven tricle has the appearance of a narrow band of white fibres, but, when the caudate body is removed, it is seen to be the margin of a tract of fibres which is derived from slips emerg ing from between the lamina of the internal capsule to increase its volume as it passes forward beneath the caudate nucleus.