from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The midbrain.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. 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 the GNU version of the Collaborative International Dictionary of English
- n. The middle segment of the brain; the midbrain. Sometimes abbreviated to mesen. See brain.
from The Century Dictionary and Cyclopedia
- n. 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 WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the middle portion of the brain
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.
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.
A broad layer of nerve-containing grey matter found bilaterally throughout the mesencephalon, or upper brain stem.
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 rhombencephalonthe last being continuous with the medulla spinalis.
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.
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).
The mid-brain or mesencephalon (Fig. 681) is the short, constricted portion which connects the pons and cerebellum with the thalamencephalon and cerebral hemispheres.
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).
The parts of mid-brain (mesencephalon) will be easily recognised.
The mesencephalon is what connects the hindbrain to the brain stem.
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