left brain n. The left cerebral hemisphere of the brain; in humans, it controls motor activity on the right side of the body, and in most people is the primary location for control of language, logic, and mathematical thought.
... line. We may regard it as a mass of representative fibres rooted in the soft substance of the convolutions or gray matter of the brain generally, and thus connecting across the median line the corresponding parts of the right and left brain. ... — Buchanan's Journal of Man, April 1887 - Volume 1, Number 3 • Various
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