commissura posterior

com·mis·sur·a pos·te·ri·or

a thin band of white matter, crossing from side to side beneath the habenula of the pineal body and over the aditus ad aqueductum cerebri; it is largely composed of fibers interconnecting the left and right pretectal region and related cell groups of the midbrain; it marks the junction of the diencephalon and mesencephalon.
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