• Webster's Revised Unabridged Dictionary
    • n. pl Lyencephala (Zoöl) A group of Mammalia, including the marsupials and monotremes; -- so called because the corpus callosum is rudimentary.
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Century Dictionary and Cyclopedia
    • lyencephala In Owen's classification, the lowest of four subclasses of Mammalia, including the marsupials and monotremes, or Didelphia and Ornithodelphia; the implacental mammals. The name indicates the loose or slight connection of the right and left hemispheres of the cerebrum, in consequence of the small size, if not the absence, of the main commissure or corpus callosum. It is correlated with Lissencephala, Gyrencephala, and Archencephala.
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Webster's Revised Unabridged Dictionary
NL., fr. Gr. to loose + the brain