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Show }. C/in. Neuro-ophthd/mol. 2: 143-144, 1982. Four rounded elevations lie on the dors.ll .lspect of the midbrain. They n1.l"'e up the qu.ldrigemin<ll plate or tectum. which is further ~ubdivid(>d into the p.lired superil)r .1Ild inferil)r wlliculi (SC. IC). The brachium of the superil)r colliculus (bs) .lIld of the inferior colliculus (bi) .In' structures which connect the midbr.lin .lnd the dienceph.llon. The brachium of the superior colliculus leads upwards and forward between the thalamus and the medial geniculate (MG). In this specimen. some of the external prominences of the thalamus are seen: lateral geniculate (lG), medial geniculate (MG), and pulvinar (pul). The lateral geniculate bodies give rise to the fibers of the geniculocalcarine tract (optic radiations). The medial geniculate bodies are the final sensory relay station of the hearing pathway. Acoustic fibers end in the nucleus of the inferior colliculus. From here axons travel to the medial geniculate body through the brachium of the inferior colliculus. The pulvinar (pul) is the large posterolateral area of the thalamus and connects reciprocally with association areas of the parietal, temporal, and occipital cortex. The pupillary fibers exit the optic tract and enter the brachium of the superior colliculus but do not enter the superior colliculus. They travel rostrally and medially into the pretectal region. Above the From the Department of Ophthalmology. Bascom Palmer Eye Institute. University of MIami School of Medicine (NBBI. and Department of Anatomy. Un,vNsity of Miami School of Med. icine (RGCI, MiamI. Florida. June 1982 Neuro-anatomical Feature Photo NORMA BOSCHETTI BARTON, M.D., Ph.D. RONALD C. CLARK, Ph.D. superior colliculus there i d depn.' sion where the pine.ll body (P) rests. The pineal is Pdft of the diencephalon. It projects over the tectum and is bC'lieved to h.lve d s('(f('tory role associated with growth .lIld d('vclopment. In the dorsal margin of thl' ba (' llf the pinedl, the hdbenular nuclei (H) are located. The habenular nudei Me Pdft of the epithalamus (narrow band on the roof of the diencephalon). These structures have afferents from the septal nuclei, olfactory nudei, and lateral hypothalamus. The caudal boundary of the midbrain is a plane passing through the fourth nerve (arrows) and the superior border of the pons. At the basilar portion of the midbrain are the cerebral peduncles (CP). The fourth nerve exits below the inferior colliculus. It is the only cranial nerve to exit at the dorsum of the brain stem and the only one to entirely decussate. The decussation occurs at the superior medullary velum (smv), the rostral portion of the roof of the fourth ventricle (IV) which lies between the two converging superior cerebellar peduncles (scp). The fourth ventricle lies dorsal to the pons. In this specimen, the cerebellum has been removed, and one can see the floor of the fourth ventricle. Its lateral walls are formed by the three pairs of peduncles which connect the cerebellum to the brain stem. In this picture. only the superior and middle cerebellar peduncles are seen (scp. mcp). Write for reprints to: Norma Boschetti Barton, M.D.. Bascom Palmer Eye Institute. P.O. Box Olb880. Miami, Florida 3310 I. 143 Journal of Clinical Neuro-ophthalmology |
