Measurement · JPCB
Posterior cranial base (S–Ar) — Jarabak
Loading the reference ceph.
Definition
The distance from Sella down to Articulare — the posterior limb of the Björk polygon (norm ≈ 32 mm adult).
How
Measure S→Ar in mm.
Purpose
Represents posterior facial 'hanging height' from the cranial base; with ramus height it builds posterior face height. Short values crowd the posterior face and push growth vertical.
High
Above the norm reads as a long posterior cranial-base limb — favors posterior face height (horizontal rotation).
Low
Below the norm reads as a short posterior limb — less posterior height, vertical tendency.
This is a reviewed tracing on one real cephalogram — the same ceph on every page in Learn — so Posterior cranial base (S–Ar) — Jarabak here is a real reading and not a diagram.