[TA] a triangular area on the lateral surface of the caudal half of the mesencephalon, bordered caudally by the slight prominence of the lateral lemniscus, dorsally by the base of the inferior colliculus and the brachium of the superior colliculus, and ventrally by the crus cerebri. SYN: lemniscal trigone, Reil triangle, triangle of fillet, trigone of fillet.
