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Several of the bones of the skull have developed air spaces that are lined with mucous membrane. It is this mucous membrane that becomes infected in sever cases of sinusitis. It is also irritation of the mucous membrane that results in excessive fluid production that can fill the air spaces and give you a stuffed nose feeling. Since these sinuses are embedded in bone, they cannot be seen easily on regular skull preparations and usually require sawing into the bone to see them. Some believe that the function of the sinuses are twofold: 1) makes the skull lighter to carry around and 2) serve as resonating chambers during speech. The figures below were taken from a specially prepared skull.
  
Once you have learned some of the bones of the skull, you should then try to visualize some areas as they project to the skin. In the following diagrams, you can see some areas of the skull as they project onto the skin of the face.
FACIAL SKULL
The sensory nerves of the face enter the face through a series of foramina:
- 1 supraorbital (supraorbital nerve & vessels) Deep to frontalis m.
- 2 infraorbital (infraorbital nerve & vessels) Deep to levator labii superioris m.
- 3 mental (mental nerve & vessels) deep to the platysma m.
- 4 zygomaticofacial (zygomaticofacial nerve)
Identify the following on the anterior skull and face
- glabella
- superciliary arch
- canine fossa
- alveolar processes
- anterior nasal spin
In cadaver dissections, the skin is removed carefully and the muscles of facial expression are identified. This is no easy task since the skin is very thin and with very little fatty tissue beneath it. The motor nerves to the muscles of facial expression and the muscles themselves are just beneath the skin. Up until now you have studied muscles that have had 2 bony attachments. The muscles of the face may have a bony attachment but the insertion is into the skin. This is how we can make facial expressions of happiness, sadness, anger or disapproving. Most of us understand these expressions well.
Once the skin is removed and the muscles cleaned, you can start to name them. In the following images, the muscles are identified.
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MUSCLES OF THE FACE
Muscles of facial expression (image 1):
- frontalis
- orbicularis oculi
- orbital portion
- palpebral portion
- zygomaticus major
- levator labii superioris alequae nasii
- levator anguli oris
- orbicularis oris
- risorius
- depressor anguli oris
- depressor labii inferioris
- mentalis
- platysma
Image 2 displays the buccinator and the masseter muscles. The masseter is a muscle of mastication, not facial expression but it is superficial in the face.
You might notice that the muscles of facial expression are arranged around the orifices of the face: orbit, nasal cavity, mouth and ear (although you wont examine these).
Muscles around the mouth include:
- zygomaticus major (3)
- levator labii superior alequae nasii (4)
- levator anguli oris (5)
- orbicularis oris (6)
- risorius (7)
- depressor anguli oris (8)
- depressor labii inferioris (9)
- buccinator
Muscles around the orbit are:
- frontalis (1)
- orbicularis oculi (2)
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MOTOR INNERVATION
TO THE FACE
The motor innervation to the muscles of facial expression is Cranial Nerve VII (Facial) (yellow in the diagram)
It leaves the skull through the stylomastoid foramen on the base of the skull and immediately turns forward to enter the substance of the parotid gland (pink in the image). While within the gland, it divides into 5 major divisions:
- T -- temporal
- Z -- zygomatic
- B -- buccal
- M -- mandibular
- C -- cervical
Another nerve enters deep in the buccal area where the buccal branches of the facial nerve are found but it is a purely sensory branch of the mandibular branch of Cranial Nerve V (Trigeminal). It supplies the mucous membrane inside the cheek and to the skin in this area. The parotid duct (white) can be seen crossing the masseter muscle on it way to penetrate the buccinator muscle. It opens into the mouth opposite the upper 2nd molar tooth. It forms a small swelling (papilla) inside the oral cavity that can be easily seen. The partotid gland is one of three salivary glands in the head and neck.
The transverse facial artery (red) runs just above the parotid duct and is a branch of the superficial temporal artery.
The arterial and venous supply to the face is seen in the diagram. They are the:
- Facial artery
- inferior labial
- superior labial
- angular
- Facial vein
- Superficial temporal artery
- Superficial temporal vein
The facial vein is important clinically because it has a direct connection to the ophthalmic vein and then to a deep venous sinus within the cranial cavity, the cavernous sinus. Bacteria can enter the facial vein and gain access to internal cranial structures resulting in infection there. This is probably the reason our mothers always said not to squeeze our pimples.
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