Structure of the Occipitofrontalis Muscle
The muscle consists of two muscular portions united by a broad, flat tendon—the epicranial aponeurosis, or galea aponeurotica (galea aponeurotica).
- Frontal belly (venter frontalis) — located in the anterior region of the cranial vault. It originates by blending into the skin of the eyebrows and runs superiorly, where it continues into the galea aponeurotica. The orbital portion of the orbicularis oculi muscle (m. orbicularis oculi) runs inferior/deep to the frontal belly.
- Occipital belly (venter occipitalis) — located in the posterior region (occipital area). It originates from the superior nuchal line (linea nuchae superior) and the mastoid process (proc. mastoideus), courses superiorly, and inserts into the epicranial aponeurosis.
The epicranial aponeurosis serves as a superficial fascia equivalent for the fronto-parieto-occipital region.
Functions
The muscle functions depend on the contraction of its respective bellies:
- Frontal belly elevates the eyebrows and forms transverse wrinkles on the forehead.
- Occipital belly pulls the scalp posteriorly and tightens the epicranial aponeurosis.
Blood Supply and Innervation
Blood supply is provided by the supraorbital, supratrochlear, occipital, and posterior auricular arteries.
The supraorbital artery (a. supraorbitalis) exits through the supraorbital notch onto the forehead and supplies the frontal belly of the m. occipitofrontalis.
Motor innervation is provided by branches of the facial nerve (n. facialis). The frontal belly receives branches including the temporal and frontal branches. The occipital belly is innervated by branches of the facial nerve, notably the posterior auricular branch.
Topography and Clinical Significance
The occipitofrontalis muscle and galea aponeurotica form the third layer of the fronto-parieto-occipital region of the head.
- Layered structure feature: The skin, subcutaneous fat, and epicranial aponeurosis are tightly bound together by dense fibrous septa. Therefore, during trauma or surgical interventions, these three layers peel away from the calvaria as a single sheet, leading to "scalp avulsion" injuries.
- Subaponeurotic space (spatium subaponeuroticum): Located deep to the epicranial aponeurosis, this layer contains loose connective tissue without fibrous septa. This space is bounded anteriorly by the attachment of the frontal belly to the supraorbital margin of the frontal bone, and posteriorly by the attachment of the occipital belly to the superior nuchal line. The loose areolar tissue facilitates the spread of infection or fluid collections.