(3.34)

This tape is the second of two that describe the head and neck. In it, we'll look first at the facial muscles and the scalp, then at the brain and its surroundings, then at the nerves and blood vessels of the head and neck, then at the eye, and the ear.

We'll start by looking at the face. Some important parts of the face, the nose and the orbit, are covered separately in these two tapes. In this section we'll focus on the facial muscles, which produce the movements of facial expression. We'll go from above down, starting with the muscle that closes the eye, the orbicularis oculi.

All this is the orbicularis oculi. It surrounds the opening between the upper and lower lids, the palpebral aperture. Orbicularis oculi has an inner or palpebral part, and an outer or orbital part. The palpebral part is extremely thin, the orbital part is more substantial.

Orbicularis oculi arises medially from this underlying structure, the medial palpebral ligament, and from the bone above and below it. Its fibers pass above and below the palpebral aperture, joining with each other here.

When the palpebral part of the muscle contracts, the eyelids close gently. When the whole muscle contracts, they close tightly. Opening the eye is caused by elastic forces acting on the lower lid, and by a more deeply placed levator muscle acting on the upper lid, that we'll see later in this tape.

Now we'll move down to look at the muscles around the mouth and the nose. The opening between the lips, the oral commisure, is surrounded by the orbiculartis oris muscle. Here's part of it. The orbicularis is joined and overlaid by several other facial muscles which we'll remove from the picture for a moment.

Here's the orbicularis oris by itself. Its more superficial fibers encircle the oral commisure, some of them arising from bone here. Its deeper fibers are continuous with those of the buccinator muscle, as we saw in the previous tape. The action of orbicularis oris is to close the oral commisure, and press the lips together.

The deep hollow here between the buccinator and masseter muscles is filled with this buccal fat pad, which is continuous with the fat that covers the front of the cheek.

Now we'll return to the picture all except one of the muscles that pull on the orbicularis oris. Pulling on it from above and behind is the zygomaticus major, which arises from here on the zygomatic bone. Pulling on it from behind is the risorius muscle. We use both these muscles when we smile.

Pulling on the orbicularis from above are zygomaticus minor, absent in this instance, levator anguli oris, and levator labii superioris. These arise from here on the maxilla. Together they raise the upper lip.

The most medial corner of levator labii superioris, which goes by this very impressive name, [levator labii superioris alaequae nasi] attaches to the alar cartilage of the nose. It does this. Here on the side of the external nose is the nasalis muscle. It helps to wrinkle the nose.