from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun The midbrain.

from The Century Dictionary.

  • noun The midbrain; a segment of the encephalon consisting essentially of the corpora quadrigemina or optic lobes and the crura cerebri. See brain. Also mesencephal, mesocephalon.

from the GNU version of the Collaborative International Dictionary of English.

  • noun (Anat.) The middle segment of the brain; the midbrain. Sometimes abbreviated to mesen. See brain.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun A part of the brain located rostral to the pons and caudal to the thalamus and the basal ganglia, composed of the tectum (dorsal portion) and the tegmentum (ventral portion).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun the middle portion of the brain


from Wiktionary, Creative Commons Attribution/Share-Alike License

From Latin, from Ancient Greek μέσος (mesos, "middle") + ἐγκέφαλος (enkephalos, "cephalon, brain"); see also cephalon.


  • It has also been understood for some time that the functions of these and several other primary reflex centers are integrated in the mesencephalon, that is, the grey matter, grouped in several nuclei, which is located below the hemispheres of the cerebrum, in immediate proximity to the hypophysis, which exercises a regulating influence on a great many vegetative functions.

    Nobel Prize in Physiology or Medicine 1949 - Presentation Speech

  • For reasons of its own, evolution allowed mammalian energy to hold sway, and the recently developed human midbrain or mesencephalon, which had folded over the old diencephalon, could be accurately labeled a mammal brain.

    La insistencia de Jürgen Fauth

  • A broad layer of nerve-containing grey matter found bilaterally throughout the mesencephalon, or upper brain stem.

    Alcohol and The Addictive Brain

  • A broad layer of nerve-containing grey matter found bilaterally throughout the mesencephalon, or upper brain stem.

    Alcohol and The Addictive Brain

  • The mid-brain or mesencephalon (Fig. 681) is the short, constricted portion which connects the pons and cerebellum with the thalamencephalon and cerebral hemispheres.

    IX. Neurology. 4b. The Mid-brain or Mesencephalon

  • The cephalic end of the neural groove exhibits several dilatations, which, when the tube is closed, assume the form of three vesicles; these constitute the three primary cerebral vesicles, and correspond respectively to the future fore-brain (prosencephalon), mid-brain (mesencephalon), and hind-brain (rhombencephalon) (Fig. 18).

    I. Embryology. 6. The Neural Groove and Tube

  • These are marked off from each other by intervening constrictions, and are named the fore-brain or prosencephalon, the mid-brain or mesencephalon, and the hind-brain or rhombencephalon—the last being continuous with the medulla spinalis.

    IX. Neurology. 2. Development of the Nervous System

  • A few fibers of the medullary stria are said to pass by the habenular nucleus to the roof of the mid-brain, especially the superior colliculus, while a few others come into relation with the posterior longitudinal bundle and association tracts of the mesencephalon.

    IX. Neurology. 4e. Composition and Central Connections of the Spinal Nerves

  • In its early embryonic condition it consists of three hollow vesicles, termed the hind-brain or rhombencephalon, the mid-brain or mesencephalon, and the fore-brain or prosencephalon; and the parts derived from each of these can be recognized in the adult (Fig. 677).

    IX. Neurology. 4. The Brain or Encephalon

  • The parts of mid-brain (mesencephalon) will be easily recognised.

    Text Book of Biology, Part 1: Vertebrata


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