Measurement · UGON
Upper gonial angle (Ar-Go-N)
Loading the reference ceph.
Definition
The upper portion of the gonial angle: the angle at Gonion between the ramus (toward Articulare) and the line to Nasion. Jarabak's split of the gonial angle.
How
At Gonion (Go), measure between Go→Ar (up the posterior ramus) and Go→N. The N–Go line splits the full gonial angle into this upper part and the lower part (N-Go-Gn).
Purpose
Jarabak used the split to localize WHERE mandibular form drives growth direction: the upper gonial angle reflects ramus inclination — its share of the gonial angle speaks to condylar (posterior) growth behavior.
High
Above the norm reads as a backward-inclined ramus — more horizontal growth vector contribution from the ramus.
Low
Below the norm reads as an upright ramus — the ramus contributes little backward inclination.
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so Upper gonial angle (Ar-Go-N) here is a real reading and not a diagram.