The occipitofrontalis is a muscle located on the skull. Also known as the epicranius, the occipitofrontalis muscle consists of two main sections called bellies. A posterior segment, named the occipital belly, is located near the rounded lower portion of the back of the head made of the occipital bone. The anterior part, known as the frontal belly, is found near the frontal bone of the cranium.
An occipital belly has two points of origin. One part begins on the occipital bone at the second nuchal line, called the superior nuchal line. A nuchal line is one of the four curved ridges visible on the outer surface of the occipital bone. The other point of origin is on the part of the temporal bone called the mastoid process that is located just above and behind the ear. It is supplied with blood through the occipital artery.
The frontal belly originates in the galea aponeurotica and the insertion is in the skin of the forehead, eye orbit, and nose. A galea aponeurotica is a layer of dense fibrous tissue that covers most of the upper skull. It is secured to the bone by a loose matrix of cellular tissue, which allows it to slide over skull with the movement of the cranial muscles. Blood is supplied to the frontal belly by the superficial temporal artery of the cranium.
Both parts of the occipitofrontalis muscle are controlled by the cranial nerve VII. This nerve supplies the message from the brain to move the facial muscles. Each belly of the occipitofrontalis is communicated with by separate branches of the seventh cranial facial nerve. The occipital belly is controlled by the superior auricular branch or the upper part of the nerve by the ear. A frontal belly is controlled by the temporal branch, which is near the part of the face called the temple.
The muscle movements of the occipitofrontalis have a large impact on the formation of facial expressions. Facial muscles responsible for the action of smiling and yawning can cause the occipital belly to move. When a person wiggles his ears, the occipital belly moves.
Involuntary contractions of this muscle also causes the development of forehead wrinkles. This occurs when the frontal belly of the occipitofrontalis muscle contracts, causing the skin of the scalp and forehead to move up and down. Then the galea aponeurotica is moved by the occipital belly, which causes the scalp to push forward.