After a long day at your desk, the tension in your shoulders and neck can creep up into your head and give you a headache. Self-massage of the muscles on your forehead and near the base of your skull can give you some relief.
Anatomically, you’re looking for the occipitofrontalis (AKA epicranium) muscle. Here’s a picture.
The frontalis part of the muscle and the occipitalis part are connected by the big tendon sheath called the galea aponeurotica (AKA epicranial aponeurosis). If there is tension in either the frontalis or the occipitalis (or both) they can pull the galea aponeurotica down on your skull like a tight skullcap.
Self-massage of the muscle tissue at either end of this system can help ease the tension in this muscle.
The frontalis pretty much corresponds to your forehead, lying between your eyebrows and your hairline. To massage the frontalis, place the palms of your hand toward your face, curve your fingers, and press the pads (not tips) of your fingers into the skin above your eyebrows. Sink in firmly and make circles with your fingerpads, moving up and down and side to side to massage all parts of the frontalis, from just above your eyebrows to your hairline.
The occipitalis muscle is on the back of your head, just above the base of your skull. Put your hands behind your head and place the pads at the base of your thumbs on the back of your neck. Find the last bit of relatively soft muscle at the top of your neck and then go up about an inch. Using the same firm curved-finger approach, massage the muscle just above the base of your skull, moving up and down and side to side to get all parts of the occipitalis.