In elevation of the eyebrows and production of transverse wrinkles of the face:
Occipitofrontalis muscle consists of two parts or bellies; the occipital belly is near the occipital bone, and the frontal belly near the frontal bone of the forehead.

Flat digastrics muscle with occipital and frontal bellies share a common tendon (epicranial aponeurosis).
Independently the occipital belly retracts the scalp, frontal belly protracts the scalp.
Simultaneously they elevate eyebrows, produce wrinkles across the forehead, surprised look.

​Key Concept:

The frontal bellies are longer, wider and partly united in the median plane. Each arises from the skin of the upper eyelid and forehead, mingling with the orbicularis oculi and the corrugator supercilii. It is supplied by the temporal branch of the facial nerve.
The muscle raises the eyebrows and causes horizontal wrinkles in the skin of the forehead.
Only the occipital bellies of occipitofrontalis act
Only the frontal bellies of occipitofrontalis act
Both the bellies act simultaneously
Both the bellies act one after the other