from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The point in the skull where the nasal and frontal bones unite.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The point at the root of the nose where the frontal and two nasal bones meet.
from the GNU version of the Collaborative International Dictionary of English
- n. The middle point of the nasofrontal suture.
from The Century Dictionary and Cyclopedia
- n. In craniometry, the median point of the nasofrontal suture. See craniometry.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the craniometric point at the bridge of the nose where the frontal and nasal bones of the skull meet
The term nasion is applied to the middle of the frontonasal suture.
On and above the glabella a trace of the frontal suture sometimes persists; beneath it is the frontonasal suture, the mid-point of which is termed the nasion.
Situated between, and connecting the superciliary ridges, is a smooth, somewhat triangular area, the glabella, below which the nasion (frontonasal suture) can be felt as a slight depression at the root of the nose.
Below the nasion the nasal bones, scantily covered by soft tissues, can be traced to their junction with the nasal cartilages, and on either side of the nasal bone the complete outline of the orbital margin can be made out.
To mark out the position of the frontal sinus three points are taken: (1) the nasion, (2) a point in the middle line 3 cm. above the nasion, (3) a point at the junction of the lateral and intermediate thirds of the supraorbital margin.
The longitudinal fissure corresponds to the medial line of the scalp between the nasion and inion.
Starting from the nasion, a line drawn along the middle of the scalp to the inion represents the superior border.
To define the central sulcus (fissure of Rolando) two points are taken; one is situated 1.25 cm. behind the center of the line joining the nasion and inion; the second is at the intersection of the line of the posterior ramus of the lateral cerebral fissure with a line through the preauricular point at right angles to Reids base line.
Another method of defining the Sylvian point is to divide the distance between the nasion and inion into four equal parts; from the junction of the third and fourth parts (reckoning from the front) draw a line to the frontozygomatic suture; from the junction of the first and second parts a line to the auricular point.
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.