#foramen__hiatus  a natural opening or perforation through a bone or a membranous structure
  supertype:  opening.space__gap  an open or empty space in or between things; "there was a small opening between the trees"; "the explosion made a gap in the wall"
  subtype:  interventricular_foramen__foramen_of_Monro__Monro's_foramen  the small opening (on both the right and left sides) that connects the third ventricle in the diencephalon with the lateral ventricle in the cerebral hemisphere
  subtype:  foramen_magnum__foramenmagnum  the large opening at the base of the cranium through which the spinal cord passes

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