from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The middle of the anterior margin of the foramen magnum of the skull.
from the GNU version of the Collaborative International Dictionary of English
- n. The middle of the anterior margin of the great foramen of the skull.
from The Century Dictionary and Cyclopedia
- n. In anatomy, the middle of the anterior margin of the foramen magnum. See cut under craniometry.
The mid-points on the anterior and posterior margins of the foramen magnum are respectively termed the basion and the opisthion.
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.
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.