Cross Section Through the Pretectal Region of the Midbrain
The pretectal region (B21) situated orally to the superior colliculi represents the tran-sition from the midbrain to the diencephalon. Hence, the cross section already contains structures of the diencephalon: dorsally on each side lies the pulvinar (B22), in the middle the epithalamic commissure (B23), and ventrally the mamillary bodies (B24). The pretectal region extends dor-solaterally with the principal pretectal nucleus(B25). The latter is an important relay sta-tion for the pupillary reflex. The fibers of the optical tract and the fibers of the occipital cortical fields terminate here. An efferent pathway of the nucleus extends across the epithalamic commissure to the Edinger – Westphal nucleus (accessory oculomotor nucleus). Ventral to the aque-duct are the Darkshevich’s nucleus (B26) and the interstitial nucleus (of Cajal) (B27), the relay stations in the system of the medial longitudinal fascicle.
Animal experiments have shown that the interstitial nucleus of Cajal and the prestitial nucleus situated further orally are impor-tant relay stations for automatic motions within the extrapyramidal motor system. The essential synapses for the rotation of the body around its longi-tudinal axis lie in the interstitial nucleus, those for raising the head and upper body in the prestitial nucleus.
B28 Supramamillary commissure.
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