Structure of the occipitofrontal muscle
The muscle consists of two muscular portions united by a wide, flat tendon—the epicranial aponeurosis, or epicranial helmet (galea aponeurotica).
- Frontal belly (venter frontalis) is located in the anterior region of the cranial vault. It originates by blending into the skin of the eyebrows and extends superiorly, continuing into the galea aponeurotica. The orbital part of the orbicularis oculi muscle (m. orbicularis oculi) runs superior to the frontal belly.
- Occipital belly (venter occipitalis) is located in the posterior region, in the occipital area. It originates from the superior nuchal line (linea nuchae superior) and the mastoid process (proc. mastoideus), extends superiorly, and blends into the epicranial aponeurosis.
The epicranial aponeurosis acts as the superficial fascia for the frontoparieto-occipital region.
Functions
The functions of the muscle depend on the contraction of its bellies:
- The frontal belly raises the eyebrows and forms transverse wrinkles on the skin of the forehead.
- The occipital belly pulls the scalp backward 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) emerges 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 directed to it, including the temporal and frontal branches. The occipital belly is innervated by branches of the facial nerve, including the posterior auricular branch.
Topography and clinical significance
The occipitofrontal muscle and galea aponeurotica form the third layer of the frontoparieto-occipital region of the head.
- Layered structure feature: The skin, subcutaneous adipose tissue, and epicranial aponeurosis are firmly connected by dense fibrous septa. Therefore, during trauma or surgical interventions, these three layers peel off the bone as a single sheet, which leads to the occurrence of "scalp" wounds of the head.
- Subaponeurotic space (spatium subaponeuroticum): A layer of loose connective tissue devoid of trabeculae lies beneath the epicranial aponeurosis. This space is bounded anteriorly by the attachment of the frontal belly of m. occipitofrontalis to the supraorbital margin of the frontal bone, and posteriorly by the attachment of the occipital belly to the superior nuchal line. The loose connective tissue contributes to the spread of inflammatory processes.
Class and exam questions
Where does the frontal belly of the occipitofrontal muscle attach?
It originates by blending into the skin of the eyebrows and continues superiorly into the epicranial aponeurosis (galea aponeurotica).
Which structure connects the bellies of the muscle?
The frontal and occipital bellies are connected by the epicranial aponeurosis, also known as the epicranial helmet.
What is the innervation of the occipitofrontal muscle?
Motor innervation is provided by branches of the facial nerve: the frontal and temporal branches supply the frontal belly, while the posterior auricular branch supplies the occipital belly.
What else to study on this topic
- Epicranial aponeurosis (galea aponeurotica)
- Subaponeurotic fascial space
- Facial nerve (n. facialis)
- Supraorbital artery (a. supraorbitalis)
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