(3.15)

Now we'll move on to look at the scalp. To understand the scalp we'll start with a dissection in which all its layers have been removed, exposing the skull.

The dome of the skull, known as the calvaria, is formed by bones that we've seen in the previous tape, the frontal, parietal, and occipital, bones, and on the side by the squamous part of the temporal bone. The temporal bone is covered by the investing deep fascia of the temporalis muscle.

Overlying the calvarium is a layer of loose connective tissue, the areolar layer. It overlies the deep temporal fascia, too. The areolar layer separates the bone from the next layer that we'll add, the assembly of structures known collectively as the epicranium. The epicranium is formed partly by tendon, partly by muscle. To see it better, we'll add all of it to the picture.

Over the dome of the skull the epicranium is formed by a sheet of tendon that's known as the galea, or galea aponeurotica. Two muscles are attached to the galea, in front, the frontalis, and behind, the occipitalis.

The occipitalis muscle arises from here on the occipital bone, above the superior nuchal line. It inserts into the galea. The frontalis muscle arises from the galea, and inserts into the skin of the lower part of the forehead, close to the eyebrow.

These two muscles produce important movements of facial expression. When occipitalis and frontalis act together, the eyebrows rise. When frontalis acts by itself, the forehead is pulled downward in a frown.

The full effect of a frown comes from the added effect of these not very separate muscles, depressor supercilii and procerus, and by the more deeply placed corrugator supercilii, which pulls the eyebrow medially causing these vertical wrinkles.

On the side of the head, the epicranium is formed by this area of dense connective tissue, the superficial temporal fascia. In some individuals, as in this this different specimen, the epicranium includes the vestigial auricularis muscles, which can move the external ear.

Now we'll add the more superficial part of the scalp to the picture. Firmly attached to the epicranium is a layer of fibrous tissue interlaced with fat. Above this is the hair bearing skin of the scalp. These are the hair follicles, which extend through the thickness of the skin.