Plural of cortex; the outer layer of the brain, or the outer layer of other organs or structures.
From Latin cortex (bark, rind, outer layer). The plural can be either 'cortices' (Latinate) or 'cortexes' (English), showing how English assimilates Latin words.
The cerebral cortex is where thinking happens—the fact that we call it the 'bark' (cortex = bark) shows how ancient anatomists compared the brain's layered structure to tree bark!
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