Definitions
from The Century Dictionary.
- noun In anatomy, the middle of the anterior margin of the foramen magnum. See cut under
craniometry .
from the GNU version of the Collaborative International Dictionary of English.
- noun (Anat.) The middle of the anterior margin of the great foramen of the skull.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun anatomy The middle of the
anterior margin of the foramen magnum of theskull .
Etymologies
from Wiktionary, Creative Commons Attribution/Share-Alike License
From Ancient Greek a base.
Support
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Examples
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The mid-points on the anterior and posterior margins of the foramen magnum are respectively termed the basion and the opisthion.
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The height is usually measured from the basion to the bregma, and the proportion of height to length (height X 100)/length constitutes the vertical or height index.
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The occipitofrontal or longitudinal arc is measured from the nasion over the middle line of the vertex to the opisthion: while the basinasal length is the distance between the basion and the nasion.
nuxiy commented on the word basion
"The point where the anterior margin of the foramen magnum is intersected by the median sagittal plane. The point is located on the inner border of the anterior margin of the foramen magnum directly opposite of opisthion. In rare cases, the determination of the position of basion may be made difficult by a thickening of the anterior margin. In height measurements of the braincase, basion is positioned somewhat farther onto the underside of the margin of the foramen magnum (hypobasion), so that the observer may distinguish between an inferior and a posterior basion for reasons of convenience and technical demands."
- SNPA
March 21, 2009