Muscles of facial expression
The muscles of facial expression are thin sheets that mostly arise from bone and insert into skin. They develop from the second pharyngeal arch, so they are all supplied by the facial nerve. They work as sphincters and dilators of the eyes, nose and mouth.
| Muscle | Attachments | Action |
|---|---|---|
| Frontalis | Epicranial aponeurosis to skin of eyebrows | Raises eyebrows, wrinkles forehead |
| Orbicularis oculi | Medial orbital margin and medial palpebral ligament, encircling the orbit and lids | Closes the eye, gently or tightly |
| Levator labii superioris alaeque nasi | Frontal process of maxilla to alar cartilage and upper lip | Flares nostril, raises upper lip |
| Levator labii superioris | Infra-orbital margin to upper lip | Raises upper lip |
| Levator anguli oris | Canine fossa of maxilla to angle of mouth | Raises angle of mouth |
| Zygomaticus major | Zygomatic bone to angle of mouth | Draws angle up and out (smiling) |
| Orbicularis oris | Encircles the mouth within the lips | Closes and purses lips |
| Buccinator | Maxilla and mandible opposite the molars, pterygomandibular raphe, to angle of mouth | Presses cheek against teeth |
| Depressor anguli oris | Oblique line of mandible to angle of mouth | Pulls angle down |
| Depressor labii inferioris | Mandible in front of mental foramen to lower lip | Pulls lower lip down |
Masseter and temporalis on the same specimen are muscles of mastication, supplied by the mandibular nerve (V3), not the facial nerve. Masseter runs from the zygomatic arch to the ramus and angle of the mandible; temporalis runs from the temporal fossa to the coronoid process.
Facial artery and vein
The facial artery is the main artery of the face. It arises from the external carotid artery just above the greater horn of the hyoid and runs deep to the posterior belly of digastric. It then grooves the back of the submandibular gland and hooks round the lower border of the mandible at the front edge of masseter, where its pulse can be felt. From there it runs a tortuous course past the angle of the mouth, giving inferior and superior labial branches, then along the side of the nose, ending as the angular artery at the medial angle of the eye.
The facial vein starts as the angular vein at the medial angle of the eye. It runs behind the artery on a straighter course, crosses the mandible and passes superficial to the submandibular gland. Below the jaw it joins the anterior division of the retromandibular vein and drains into the internal jugular vein.
The facial vein connects with the cavernous sinus in two ways: through the angular and ophthalmic veins, and through the deep facial vein and pterygoid plexus. The superficial temporal artery, the other terminal branch of the external carotid, crosses the zygomatic arch in front of the tragus.
Submandibular gland and its relations
The submandibular gland is a mixed serous and mucous salivary gland in the submandibular (digastric) triangle, lying partly under the body of the mandible. It is folded round the free posterior border of mylohyoid. A large superficial part lies below mylohyoid, and a small deep part lies above it in the floor of the mouth.
- Superficial relations: skin, platysma, investing fascia, the facial vein and the marginal mandibular branch of the facial nerve.
- Deep relations: mylohyoid and hyoglossus, with the lingual nerve above and the hypoglossal nerve below.
- Submandibular (Wharton's) duct: about 5 cm long. It leaves the deep part and runs forward between mylohyoid and hyoglossus, then between the sublingual gland and genioglossus, and opens on the sublingual papilla beside the frenulum of the tongue. The lingual nerve crosses it from lateral to medial by looping under it.
Secretomotor fibres come from the facial nerve through the chorda tympani, travel with the lingual nerve and synapse in the submandibular ganglion. Lymph drains to submandibular nodes on and in the gland.
Innervation of the face
The face has a motor supply from the facial nerve and a sensory supply from the trigeminal nerve.
After leaving the parotid, the facial nerve's upper (temporofacial) division gives the temporal and zygomatic branches, and its lower (cervicofacial) division gives the buccal, marginal mandibular and cervical branches.
- Zygomatic branches: cross the zygomatic bone to orbicularis oculi.
- Buccal branches: run forward with the parotid duct to buccinator and the muscles of the upper lip.
- Marginal mandibular branch: runs along the lower border of the mandible under platysma.
Skin sensation comes from the ophthalmic (V1), maxillary (V2) and mandibular (V3) divisions of the trigeminal nerve. The skin over the angle of the mandible is supplied by the great auricular nerve (C2, C3).
Clinical relevance
Nerve injuries, infection spread and stones are the main clinical themes of this region.
- Facial nerve palsy: a lower motor neurone lesion, such as Bell's palsy, weakens the whole half of the face. An upper motor neurone lesion, such as a stroke, spares the forehead, because the forehead muscles receive input from both hemispheres.
- Marginal mandibular injury: the lower lip cannot be pulled down on that side, giving an asymmetric smile. Submandibular incisions are made two finger-breadths below the mandible for this reason.
- Danger area of the face: infection around the nose and upper lip can reach the cavernous sinus through the angular and ophthalmic veins.
- Submandibular stones: most salivary calculi form here, because the saliva is thicker and the duct runs upwards.
- Ludwig's angina: spreading cellulitis of the submandibular and sublingual spaces, usually dental in origin, which lifts the tongue and threatens the airway.
On the specimen
The specimen is a superficial dissection of the face and upper neck with the skin removed.
- Facial artery or vein: the artery is tortuous, thick-walled and in front; the vein is straighter, thinner and behind it.
- Zygomaticus major or levator labii superioris: zygomaticus major runs obliquely from the cheekbone to the angle of the mouth; the levators run more vertically to the upper lip, with levator labii superioris alaeque nasi most medial beside the nose.
- Depressor anguli oris or depressor labii inferioris: depressor anguli oris is the superficial triangular muscle at the angle; depressor labii inferioris is medial and partly deep to it.
- Masseter or buccinator: masseter is the thick vertical muscle over the ramus; buccinator is deep in the cheek, with horizontal fibres pierced by the parotid duct.
- Submandibular or parotid gland: the submandibular gland is below the body of the mandible; the parotid is in front of the ear.