The structure indicated is the frontal belly of the occipitofrontalis muscle.
The occipitofrontalis muscle is involved in facial expression and is comprised of two muscle bellies:
- Frontal belly
- Occipital belly
Contraction of the frontal belly causes wrinkling of the forehead and raising of the eyebrows. Contraction of the occipital belly pulls the scalp back posteriorly. As a muscle of facial expression, the occipitofrontalis muscle is innervated by the facial nerve (cranial nerve VII).
In between the frontal and occipital bellies, is an aponeurotic tendon which connects two bellies.
Learn more about the muscles of facial expression in this tutorial.