foramen magnum

English Thesaurus

1. the large opening at the base of the cranium through which the spinal cord passes (noun.body)

hypernym	:	foramen, hiatus,
definition	:	a natural opening or perforation through a bone or a membranous structure (noun.body)

part meronym	:	braincase, brainpan, cranium,
definition	:	the part of the skull that encloses the brain (noun.body)