Coronal Sections of Deep Nuclei. The hippocampus, fimbria, and the gray and white matter below the temporal horn have been removed. A yellow arrow indicates the white radiations. B, Section 5 mm behind the limen that crosses the anterior part of the amygdala, but does not cross the temporal horn or the optic radiations. C and D, Gray and white matter below the temporal horn has been removed to expose the optic radiations and Meyer’s loop. The red bracket shows the area of the optic radiations in the roof of the temporal horn and the blue arrow shows the safe area between the optic radiations and the optic tract. The triangular safe area, between Meyer’s loop and the optic tract, is outlined in yellow. C, Section 10 mm behind the limen that crosses the amygdala and the anterior edge of the optic radiations. An incision directed straight downward from the inferior insular sulcus to the temporal horn would cross the radiations and temporal horn. To avoid the optic radiations, the incision would need to be directed downward and medially through the amygdala into the temporal horn. D, Anteroinferior view of the corneal section 10 mm behind the limen insula. The Meyer’s loop passes forward from the lateral geniculate body. The posterior part of the amygdala has been preserved. An incision in the inferior insular sulcus at this level would need to be directed medially (A) to avoid the optic radiations. The probe is on the medial edge of Meyer’s loop. The blue line shows the safe area between Meyer’s loop and the optic radiations. The yellow lines outline the triangular area through which the temporal horn can be entered through the floor of the sylvian fissure without damaging the optic radiations or optic tract. The safe area for entering the amygdala and temporal horn is widest anteriorly at the level of the amygdala and narrows posteriorly as the lateral geniculate is approached. An incision in the inferior insular sulcus at the level of the lateral geniculate body would cross the optic radiations as they exit the geniculate. E, At this level, 15 mm behind the limen insula, an incision directed straight downward from the inferior insular sulcus would cross the optic radiations in the roof of the temporal horn, and if directed too far medially, the incision could damage the optic tract or the lower part of the lenticular nucleus. F, At this level, 20 mm behind the limen, the area between the medial edge of Meyer’s loop and the optic tract is very small. An incision, if directed downward, would cross the optic radiations or, if directed too far medially, would damage the optic tract. An incision directed downward and medially through the inferior insular sulcus to the temporal horn, at the 25-mm level, would cross the optic radiations or damage the lateral geniculate body. (Images courtesy of AL Rhoton, Jr.)