from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The point in the human brain at which the fourth ventricle narrows to become the central canal of the spinal cord.

from The Century Dictionary and Cyclopedia

  • n. A barrier; hence, a preventive.
  • n. In anatomy, a thickening at the point of the calamus scriptorius in the membrane roofing the fourth ventricle.


From Latin ōbex ("barrier, wall"). (Wiktionary)


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  • n.¹, An impediment or obstacle; a mental barrier.
    n.², (Anatomy) A small, crescentic fold of white matter that covers the inferior angle of the floor of the fourth ventricle.

    September 6, 2008