PROCEDURE
1.
PRE-WORK
(before lab) review the major bony regions of the face from your
atlas or on an articulated skeleton in the lab.
(Netter022)
(Netter024)
(Netter011)
(Netter013)
Mandible - The body of the mandible extends laterally and posteriorly to each side forming a horseshoe-like shape holding the teeth. Posteriorly the mandible turns sharply superiorly at the angle, with the superior extension forming the ramus.
Zygomatic arch (cheek bone) - The zygomatic arch is a transverse span of bone extending from the temporal bone at the lateral side of the skull near the ear anteriorly to the rim of the orbit.
Temporal bone - The temporal bone is situated at the lateral side of the skull and houses the auditory structures. The outer margins of the bone form part of the temple, the zygomatic arch, and the inferoanteriorly directed styloid process.
Seven of the cranial nerves and the major input/output vessels of the brain all pass through foramina of the temporal bone. We will study many of these in coming lab sessions.
Mastoid process - This is a conical bump of bone immediately posterior to the ear. The superior end of the sternocleidomastoid muscle attaches to this bone.
NOTE: At your dissection tables you will have a sagittal sectioned hemi-head in the translucent organ box as well as your donor.
The steps described below should be performed on the left, right, and hemi-head giving three preparations of the superficial face region. Place the hemi-head on a plastic tray (you should find trays underneath your organ box) to provide a stable work surface.
2. Place two stacked wood blocks under the donor's head (i.e. in a pillow like position).
This elevates the donor's head off the table surface facilitating access. At times you may find it easiest when working on the lateral face to be seated on one of the metal stools.
3. Grasp the auricle (pinna) of the ear and bend the ear
anteriorly so you can access behind the ear.
(Netter008)
4. Using a scalpel, cut through the skin and connective
tissue around the base of the ear reflecting the ear anteriorly as you cut.
(Figure755) (Netter008)
(Photo7063)
As you reflect the ear, the cartilage of the auricle will separate easily from the skull, as only loose connective tissue and skin hold this part of the cartilage to the head.
The amount of skin and connective tissue holding the ear against the skull varies considerably among individuals, resulting in variation in how the auricle is situated (i.e. angled close or far from the skull).
5. Extend the incision inferiorly around to the anterior
(in front) of the ear.
(Figure755) (Netter008)
(Photo7063)
As you cut through the skin your scalpel will encounter the cartilage tube that forms part of the external auditory meatus (canal of the ear).
6. Cut through the cartilage tube of the external auditory meatus and continue superiorly such that you can completely detach the ear.
NOTE: Each donor has a metal tag attached to one ear which serves as one of the identifiers for the individual at your table. When you remove the ear, take care to retain the ear within the plastic coverings with your donor.
A tag with the hemi-head would remain within the biohazard bag with the hemi-head.
7. Follow the sternocleidomastoid muscle superiorly,
removing any fascia/skin as required, to find the mastoid process of the skull.
(Figure755) (Netter036)
(Photo7064)
This process is located approximately at the level of the earlobe posterior to the external auditory meatus.
In the hemi-head, since the skin is present around the neck you will need to dissect to expose the muscle. Remove any skin and superficial fascia from all of the regions inferior to the mandible so that you can expose the sternocleidomastoid muscle.
8. The next steps remove skin across the face and examine the muscles of facial
expression.
(Figure759)
(NetterBP020) (Netter031)
The skin of the face is thin skin with the muscles of facial expression embedded in a poorly defined layer of the underlying connective tissue (superficial fascia).
These muscles are thin and often indistinct depending on the individual. Thus, you may not be able to define the entirety of each muscle. In cases, you may only see parts of the muscle fibers blending into the connective tissue deep to the skin. A good guide to identification of the muscles is to establish the direction of the muscle fibers, as each muscle exhibits a unique orientation between its origin and insertion.
These muscles arise from bone, connective tissue, or from other muscles. All of them have insertions/connections into the skin allowing coordinated contraction of the muscles to modify the position of skin over the face in order to form expressions. The muscles are mostly named for their principal actions or bony relationships.
All of the muscles of facial expression receive facial (VII) nerve innervation. Any facial surgery strives to preserve this neural innervation, if possible, as facial paralysis has significant cosmetic and functional complications.
We will examine the main muscles of facial expression. There are other smaller muscles which we will not be dissecting specifically.
9. Grip the edge of skin on the anterosuperior side of
the opening formed by removal of the ear and begin reflecting skin in a superior
'wedge'.
(Figure756)
(Photo7065)
Note, in this and subsequent skin removal steps don't try to make an incision along the diagram cut lines all at once as you won't be able to determine cut depth. Instead, gradually extend each incision line as you reflect skin (starting at the ear opening and proceeding towards the midline) so that you can gauge and adjust the depth of the dissection.
This superior wedge of skin being removed should span directly superiorly over the skull and anteriorly to the corner of the eye. If you contact/expose the bone of the skull then you are dissecting too deeply.
Over the region of the skull a strong aponeurosis, the galea aponeurotica, spans from anterior to posterior. This aponeurosis forms a major part of the scalp coursing posteriorly over the crown of the head to the occipital bone.
As you reflect the skin, you may observe superficial temporal veins which course anterior to the ear. Any veins posterior to the ear are called posterior auricular veins.
The superficial temporal and any posterior auricular veins drain into the retromandibular vein (retromandibular meaning behind and posterior to the mandible) at a point just inferior to the earlobe. The retromandibular vein, in turn, will drain into the external jugular vein. These, along with the facial vein, form a superficial network of venous return from the face.
10. As you approach the eye, continue the skin removal in an
arc just inferior to the line of the eyebrow such that you can remove the eyebrow with the
skin.
(Figure756)
(Figure759)
(NetterBP020)
(Photo7065)
As you work across this arc you may start to see muscle fibers mixed in with the connective tissue. These are muscle fibers of the orbital part of the orbicularis oculi muscle. Clean sufficient connective tissue to observe these fibers.
Orbicularis oculi muscle - this muscle acts similarly to a
sphincter muscle consisting of a
palpebral part (for blinking the eyelid) extending onto the eyelids and an outer orbital part
(for tight closure of the eyes) with the superior part deep to the
eyebrows.
11. As you approach the midline across the forehead examine
the connective tissue deep to the skin for fibers of the thin frontalis muscle.
(Figure759)
(NetterBP020) (Netter031)
(Photo7065)
(Photo7034)
Frontalis muscle - this muscle
12. When the left and right incisions (or single side on the
hemi-head) meet at the midline detach the superior wedge of skin completely.
(Figure756)
13. Return to where you had removed the ear and begin
reflecting skin in a mid-face wedge from the anterior side of the opening.
(Figure757)
(Photo7066)
This wedge should span from where you removed the superior wedge and go anteriorly towards the corner of the mouth.
The wedge should be superficial to the parotid gland. If you cut into lobular glandular tissue then you are dissecting too deeply.
14. As you approach the eye continue to remove the skin in an
arc inferior to the eye leaving the lower eyelid intact.
(Figure757)
(Figure759)
(NetterBP020)
(Netter031)
(Photo7066)
(Photo7034)
As you work around this arc you may start to see muscle fibers mixed in with the connective tissue. These are muscle fibers of the inferior part of the orbicularis oculi muscle. Clean sufficient connective tissue to observe these fibers.
Orbicularis oculi muscle - this muscle acts similarly to a
sphincter muscle consisting of a
palpebral part (for blinking the eyelid) extending onto the eyelids and an outer orbital part
(for tight closure of the eyes) with the inferior part deep to the skin
over the superior side of the inferior orbital rim.
15. As you approach the nose, detach the skin wedge along
the side of the nose leaving the nostrils intact.
(Figure757)
(Photo7066)
With the superior and inferior skin removed around the orbit, you can appreciate the sphincter-like organization of the orbicularis oculi muscle encircling the eye.
16. As you approach the corner of the mouth, continue
removing skin from the upper lip.
(Figure757)
(Figure759)
(NetterBP020)
(Netter031)
(Photo7066)
(Photo7033)
As you work across the upper lip, you may start to see muscle fibers mixed in with the connective tissue. These fibers are the superior part of the orbicularis oris muscle. Clean sufficient connective tissue to observe these fibers.
Orbicularis oris muscle - this muscle is often described as a circular sphincter deep to the lips that surrounds the mouth. However, usually the muscle exists as multiple partly overlapping fascicles encircling the mouth (for our purposes we will treat it as a single entity).
The complex overlapping fascicle organization is essential in allowing the wide range of motion necessary to form the lips into different shapes (puckering the lips when all fascicles are contracted simultaneously).
17. When the left and right incisions (or single side on the
hemi-head) meet at the midline, detach the mid-face wedge of skin completely.
(Figure757)
(Photo7066)
The skin around the nasal opening adheres tightly to the subcutaneous connective tissue, but the skin can be detached approximately around the nasal openings.
18. Return to where you had removed the ear and begin
reflecting skin in an inferior wedge from the anterior side of the opening.
(Figure758)
(Photo7067)
This wedge should span from where you removed the mid-face wedge and span anteriorly along the mandible matching up with the area of skin removed over the neck. In the hemi-head, the skin of the neck has not been removed, so proceed with removing that neck skin to match the dissection of the donor.
Note that the facial artery crosses the mandible approximately half way between the midline of the chin and the angle of the mandible. Try not to cut that artery as you remove the skin.
As you remove the skin, you may observe fibers from the platysma muscle which cross superiorly from the neck over the mandible to insert into the skin and fascia of the cheek (some fibers insert into the inferior border of the mandible bone, but most end in the fascia of the cheek).
Although most of the platysma muscle is present in the neck and often grouped with neck muscles due to that location, the platysma muscle is innervated by branches of the facial (VII) nerve. Thus, the platysma muscle is considered a muscle of facial expression due to its common facial (VII) nerve innervation.
19. As you approach the corner of the mouth, continue
removing skin from the lower lip out to the mental protuberance (chin).
(Figure758)
(Figure759)
(NetterBP020)
(Netter031)
(Photo7067)
(Photo7032)
As you work across the lower lip, you may see the fascicles of the inferior part of the orbicularis oris muscle. Clean sufficient connective tissue to observe these fibers.
Orbicularis oris muscle - this muscle is often described as a circular sphincter inside the lips that surrounds the mouth. However, usually the muscle exists as multiple partly overlapping fascicles encircling the mouth (for our purposes we will treat it as a single entity).
20. When the left and right (or single side on the
hemi-head) meet at the midline detach the inferior wedge of skin completely.
(Figure758)
(Photo7067)
21. Dissect into the inferior lip to the corner of
the mouth where fibers of the depressor labii inferioris oris muscle insert.
(Figure759)
(NetterBP020) (Netter031)
(Netter055)
(Photo7032)
Depressor labii inferioris muscle - this muscle is located lateral to the lower lateteral aspect the mouth angled to the mandible. Contraction depresses the lower lip (e.g. forming a frown).
This is often not a distinct muscle, but rather individual fascicles angled inferolaterally from the lower lip.
22. Dissect into the superior lip lateral to
the nose at an angle towards the zygomatic arch to find the zygomaticus major
muscle
(Figure759)
(NetterBP020) (Netter031)
(Netter055)
(Photo7146)
Zygomaticus major muscle - this muscle arises from the zygomatic arch and inserts into the corner of the mouth. Contraction of the muscle draws the angle of the mouth superiorly and posteriorly (into a smile).
Zygomaticus minor muscle - this muscle is immediately medial to the major muscle and follows a very similar path. The zygomaticus minor muscle is small and difficult to distinguish from the nearby zygomaticus major muscle. Thus, we will not dissect it specifically, but you may see it in some individuals as a second bundle parallel to the zygomaticus major muscle.
23. Search along the inferior margin of the mandible,
approximately half way along its length, for the facial artery crossing over the
anterior side of the mandible.
(Figure760)
(Netter042)
(Photo7035)
The facial artery exhibits considerable variability in the terminal branching/anastomosing pattern among individuals. Branches are named by where they go, regardless of their origin pattern.
As an assistance to visualizing the cross of the facial artery over the mandible, on yourself, clench your teeth and feel the contractions of the masseter muscle at the angle and ramus of the mandible. Press your finger on the body of the mandible at the anterior edge of the masseter and feel for the facial artery pulse.
The facial vein is typically located just posterior to the facial artery at this location. Branches from the more anterior superficial veins of the face join to the facial vein.
24. Using blunt dissection follow the course of the facial
artery superiorly where it passes approximately 1.5cm lateral to the corner of
the mouth.
(Figure760)
(Netter042)
(Photo7035)
(Photo7036)
The facial artery is highly tortuous or coil-like. This tortuosity allows the vessel to accommodate spatial movements when opening and closing of the mouth. With the mouth fully open, the vessel straightens out. When the mouth closes, the vessel resumes a tortuous path.
Along the ramus of the mandible the marginal mandibular branch of the facial nerve courses lateral (superficial) across the facial artery.
25. Continue following the facial artery to where it gives off
the superior labial artery and inferior labial artery.
(Figure760)
(Netter042)
(Photo7036)
The inferior labial artery courses into the lower lip and the superior labial artery into the upper lip.
26. Continue following the facial artery superiorly where
it passes deep to the zygomaticus major muscle.
(Figure760) (Netter042)
(Netter083)
At this point the facial artery is renamed the angular artery. Do not follow it further at this time.
The angular artery terminates in anastomoses with branches of the infraorbital artery emerging from the region of the orbit linking the superficial (facial artery) supply with the deeper (maxillary artery) supply.
27. Clean soft fascia from the region anterior to the ear
until you find the dense fascia surrounding the parotid gland.
(Figure760) (Netter054)
(Photo7037)
The parotid gland lies superficial to the medial and lateral aspect of the ramus of the mandible.
The boundaries of the gland are obscured by this dense investing fascia surrounding the gland (often called the parotid capsule).
This dense fascia will not yield easily to blunt dissection and you may need to use a scalpel tip as you would normally use a probe to part the sheath and observe glandular tissue.
28. Dissect into the fascia at the anterior margin of the
parotid gland at the point in line from the corner of the mouth to the earlobe
to look for the parotid duct.
(Figure760) (Netter054)
(Photo7038)
The parotid duct is approximately 2-3mm in diameter extending from the parotid gland in line from the earlobe to the corner of the mouth.
The region of the cheek anterior to the parotid gland where the parotid duct runs contains the bulk of the buccal fat pad. This fatty tissue surrounds the parotid duct and 'fills in' the depression bounded by the masseter, zygomaticus major, and depressor labii inferioris muscles.
If you pinch your cheek between a finger and thumb (not while wearing gloves from the lab!) you can feel this softer fatty tissue making up the anterior part of the superficial cheek.
You may find small branches of the facial nerve emerging from the anterior edges of the parotid gland. Try to leave those intact if you find them as we will be examining that nerve in the next lab session.
29. Clean the duct so that you can observe that it courses
anteriorly then
turns medially to penetrate the buccinator muscle.
(Figure760) (Netter054)
(Netter055)
(Photo7039)
Don't try to follow it through the buccinator muscle into the mouth at this time.
The duct opening into the mouth is approximately adjacent to the maxillary 2nd molar tooth. If you feel with your tongue, or observe in a mirror, you may be able to find the parotid duct opening in your own mouth.
Buccinator muscle: The tissue of the cheeks contains the deepest muscle of facial expression, the buccinator muscle. The muscle is thin and quadrilateral in shape forming the 'deep cheek'. Contraction compresses the cheek against the molar teeth, keeping food on the surfaces of the teeth and the cheek taut to prevent cheek mucosa being bitten while chewing.
30. Examine the anterior edge of the parotid gland where
you will see the anterior edge of the masseter muscle, upon which the parotid
gland is sitting.
(Figure760) (Netter054)
(Netter055)
(Photo7039)
Don't dissect or clean fascia away posteriorly over the masseter muscle as that would damage facial nerve branches we will examine in the next session. For now, note that the parotid gland rests superficial (i.e. lateral) to the muscle.
31. The main sources of sensory innervation of the
superficial and deep face come from terminal branches of the trigeminal (V)
nerve.
(Netter009)
(Netter042)
We will not dissect for these branches, but note that, unlike much of the body, in the face sensory and motor nerves arise from different locations and take different trajectories into the face.
The three major branches of cutaneous sensory innervation are the supraorbital (branch of V1), infraorbital (branch of V2), and mental (branch of V3).
These nerves arise intracranially and gain access from the skull out onto the face via foramina bearing the same names as the nerve divisions themselves. These foramina are all approximately 2-3cm lateral to the midline of the skull which you observed in the skull lab.
Similarly named arteries and veins emerge with the nerves (the supraorbital, infraorbital, and mental vessels), but these structures are too small to distinguish separately from the nerve.
Post-Lab Daily Clinical Review Cases
Each lab has several multiple choice practice cases to reinforce understanding of the material within the lab and associated lectures. These are optional to review at home for consolidating and testing understanding.
CHECKLIST
Skeletal Structures
Mandible
Body
Ramus
Angle
Mental foramen
Skull
Zygomatic bone
Zygomatic arch
Temporal bone
Mastoid process
Supraorbital foramen/notch
Infraorbital foramen
Soft Structures
Ear
Auricle
External auditory meatus
Muscles of Facial Expression
Orbicularis oculi muscle
Orbital part
Palpebral part
F
Orbicularis oris muscle
Platysma muscle
Depressor labii inferioris
Zygomaticus major muscle
Buccinator
Facial artery (and vein)
Superior
labial artery
Inferior labial artery
Angular artery
Parotid gland
Parotid duct