The occipitofrontalis is the complete epicranial muscle, consisting of the frontal belly (frontalis) anteriorly and the occipital belly (occipitalis) posteriorly, connected by the galea aponeurotica. The galea is a strong fibrous sheet that allows the two muscle bellies to act as a single unit moving the scalp across the skull, which has no rigid attachment to the scalp allowing the scalp to slide freely over the underlying periosteum.
| Origin | Lateral two-thirds of the superior nuchal line and adjacent temporal bone; No bony origin, continuous with the frontalis skin attachment |
|---|---|
| Insertion | Both bellies insert into the galea aponeurotica, the epicranial aponeurosis covering the skull vault |
| Nerve Supply | Posterior auricular branch of the facial nerve (CN VII) for the occipital belly; Temporal branch of CN VII for the frontal belly |
| Blood Supply | Occipital artery (occipital belly) and supraorbital artery (frontal belly) |
| Actions |
|
|---|
The looser attachment of the scalp to the underlying periosteum, the dangerous space, allows the two muscle bellies to shift the scalp freely over the skull. In the clinical context, this layer is the plane through which subgaleal haematomas spread widely and through which scalp avulsions occur.
Scalp lacerations that extend through the galea aponeurotica gape widely and require separate galeal sutures to reduce tension on the skin closure and prevent scar widening. Subgaleal haematomas in neonates from vacuum extraction or cephalopelvic disproportion spread across the entire scalp because the blood dissects within the loose areolar tissue deep to the galea but external to the periosteum.
The frontal belly is palpable over the forehead (see frontalis). The occipital belly is palpable at the back of the skull between the mastoid and the midline, becoming firm when the scalp is actively retracted posteriorly.
Full-thickness scalp wound involving the galea producing wound gaping that requires galeal repair to reduce tension and prevent scar widening.
