Fig. 2. Diagrammatic section of brain stem. A. Cross-section at level of superior colliculus. (N-III, oculomotor nucleus; MLF, medial longitudinal fasciculus; LEM, medial lemniscus; RN, red nucleus; SN, substantia nigra; CS, corticospinal tract) B. Cross-section at level of abducens nucleus (N-VI). (PPRF, pontine paramedian reticular formation [note that reticular formation continues rostrally and caudally (arrows)]; N-VII [FN], facial nucleus; VN, vestibular nuclear complex; SNT, spinal nucleus of trigeminal; STT, spinal tract of trigeminal; STH, spinothalamic tract)