The medial geniculate body is a complex of three major nuclei (Figs. 8.1–8.3): ventral or principal, medial or magnocellular, and dorsal or posterior. The ventral nucleus lies lateral to the brachium of the inferior colliculus as this traverses the complex. It consists usually of medium-sized, tightly packed, and darkly staining cells that have a tendency to form dorsoventral rows. The medial or magnocellular nucleus lies medial to the brachium, in the angle between the brachium and the medial lemniscus. Usually, it contains relatively few cells, the most obvious of which are deeply staining, angular, and large, thus accounting for the name, but populations of smaller cells of the adjacent posterior complex tend to invade it and some workers recognize intrinsic small cells as well. The dorsal nucleus caps the ventral nucleus and expands posteriorly so as to fill the whole cross-sectional area of the medial geniculate body at its posterior pole (Figs. 8.2B and 8.3A). It usually consists of small- to medium-sized cells that are paler staining and less densely packed than those in the ventral medial geniculate nucleus.