PROCEDURE

1. Uncover your donor by opening the various layered coverings, when finished for a session the coverings are replaced in the reverse order.

Remove the blue drape, fold the drape and place it under your table.

Unzip the white body bag.

Unclip and open the clear inner plastic lining.

Your donor is covered by moist cloths which should always be left covering areas of the patient you are not dissecting during a session. This is respectful of patient dignity and protects against dehydration. The cloth should be remoistened with wetting agent frequently as needed to limit dehydration. 

Note, your donor has undergone study with the MS2 class on musculoskeletal systems. Take a moment to check the patient chart to see if there are new findings that have been made with your donor

2. Turn the donor to the supine position (i.e. on their back) taking care with the limbs due to the musculoskeletal study having removed much of the limb skin.

When turning a donor over, turn just the donor leaving the inner and outer plastic sheets as they are so that they can be closed readily after the donor is turned to the supine position.

3. Place place two stacked wood blocks under the donor's donors head (i.e. positioned like you would a pillow).

This elevates the donors head off the table surface and tilts the head anteriorly facilitating access.

At times you may find it easiest when working on the lateral face to be seated on one of the metal stools.

4. Take out the dry skull from the clear container under your table and examine the bony features of the face in parallel with the donor's face to appreciate how the bony architecture shapes the soft tissue features of the face in the steps below.

When not examining the skull, the skull should be placed back into the box to protect it.

Please exercise care with the skulls and always place them on a stable location on the table or shelf so as to avoid risk of the skull falling and being damaged.

Skulls are available for study only within the laboratory, they may not be removed from the laboratory. 

PROCEDURE - Face

5. Examine the forehead region of the donor and on the dry skull for the frontal eminence.
    (Netter008) (Netter011) (Photo7137)

The frontal eminence is a bony protuberance on the frontal bone several centimeters superior to the orbital rim. The eminences vary widely between individuals and give shape to the forehead below the hair line.

Superior to the frontal eminence the bone of the skull is smooth to allow the galea aponeurotica to 'slide' smoothly forwards and backwards when contracting the frontalis or occipitalis muscles.

6. Examine the glabella.
    (Netter008) (Netter013) (Netter011) (Photo7137)

This is the smooth area of the forehead above and between the eyebrows. This is a common area for patients to receive Botox injections to remove what are called '11' wrinkle lines

The skin of the glabella may be used clinically to test skin turgor in suspected cases of dehydration by gently pinching and lifting it. When released, the glabella of a dehydrated patient tends to remain extended, rather than returning to its normal shape.

7. Examine the orbital rim.
    (Netter008) (Netter013) (Netter011) (Photo7137)

The orbit is divided into a superior orbital rim and an inferior orbital rim. Run your fingers along each rim on the donor to palpate the margins of bone under the skin.

The frontal bone forms the forehead and all of the supraorbital rim. This is more visible on the dry skull where the skin is absent and the suture lines between the plates of bone are visible.

In males, there is a prominent supraorbital ridge (also known as the superciliary arch) while in females this ridge is less prominent. Examine your skull and observe whether there is a prominent ridge (likely male) or a smoother surface (likely female).

Along with the pelvis, the supraorbital ridge is one of the more reliable bony features for determining the phenotypic sex of bony remains. However, the prominence of the arch does vary considerably among individuals and between ethnic groups. Thus, it can be unreliable to determine sex from bone architecture alone and forensic pathologists will need to extract DNA.

8. Examine the eyelids on your donor.
    (Netter008) (Netter013) (Netter011)

Eyelids are tightly attached to the bone of the lateral and medial margin of the orbital rim, called the medial and lateral canthus.

Eyelids can freely move superiorly and inferiorly (i.e. when blinking) but are anchored to the medial and lateral orbital rim. The eyelids are secured to the bone by small tendons, the lateral and medial canthal tendons deep to the skin. 

Open an eyelid on our donor and give a gentle pull to demonstrate the lateral and medial attachments. These also form attachment regions for the palpebral part of the orbicularis oculi facial muscle.

9.  Examine the nose.
    (Netter008) (Netter013) (Netter011) (Photo7137)

The nose consists of the superior 1/3rd formed by the nasal bones and the anteroinferior 2/3rd formed by cartilage.

On the donor (or yourself) you can feel the cartilaginous anterior part of the nose. On the skull, the cartilaginous region has been removed and only the bony superior 1/3rd is visible.

A 'broken nose' is usually a fracture of the nasal bones over the bridge of the nose or in the cartilaginous portion of the nose due to an external impact. This is the most common craniofacial fracture point (~65% of all head fractures) and usually heals with minimal intervention. Fractures involving deeper bones of the nasal region are usually treated surgically.

10. Examine the cheek.
    (Netter008) (Netter013) (Netter011) (Photo7138)

The cheek is primarily shaped by the maxilla and zygomatic bones that form the inferior orbital rim.

These bones meet approximately in the middle of the inferior orbital rim. The zygomatic bone extends further laterally from this point to form the zygomatic arch connecting to a protrusion of the temporal bone. The junction points are fused tightly and often not clearly visible on the skull.

Observe the space posterior to the lateral orbital rim and deep to the zygomatic arch forming the temporal fossa. The temporal fossa is completely filled with the temporalis muscle such that in the living the lateral side of the head appears 'smooth' with the skin passing from the orbital rim over the temporalis muscle.

11. Examine the maxilla.
    (Netter008) (Netter013) (Netter011) (Photo7137)

The maxilla bone (commonly called the cheek bone) houses the superior teeth and forms part of the nasal bones and orbital rim. 

Essentially, the maxilla bone along with the zygomatic bone form the 'mid-face' bony architecture.

On the skull observe the depressions for each of the teeth and on the donor retract the upper lip sufficiently to observe the teeth. Note, in many aged individuals teeth may have been removed and the patient utilizes dentures or implants.

Since we are not in Dental school, this is the extent of our consideration of teeth structure.

12. Examine the ear.
    (Netter008) (Netter013) (Netter011) (Photo7138)

On the skull, there is a bony depression forming the external acoustic meatus, also known as the auditory canal. In the living, approximately 2/3rd of the auditory canal is bone and the other 1/3rd cartilage (opposite ratio to the nose).

The ear will be covered in a later lecture, but the major regions are the helix of the ear superoposteriorly, the lobule (a.k.a. lobe) of the ear inferiorly, and the cartilage of the tragus anterior to the auditory canal (external acoustic meatus).

Palpate the cartilage of the tragus where it comes to a point anterior and slightly inferior. This can be hard to determine in a donor with the increase in tissue rigidity. This 'tragal pointer' is commonly used to find the facial nerve in craniofacial surgery.

On yourself at a later time palpate your tragus and you will feel the distinct tragal pointer location anteroinferior on the tragus.

Palpate inferoposterior to the external acoustic meatus for the mastoid process and examine that point on the skull. The mastoid process is the bony protuberance serving as attachment for the sternocleidomastoid muscle.

13. Examine the mandible.
    (Netter008) (Netter013) (Netter011)
    (Photo7137) (Photo7138)

The mandible, or lower jaw, forms an articulation with the temporal bone at the temporomandibular joint.

On the skull, examine the condyle of the mandible where a smooth articular surface is present. Note the fossa on the skull forms a depression, the mandibular fossa. The articular surface of the condyle fits into this depression. Anterior to the head of the mandible is the coronoid process, where the temporalis muscle attaches.

Holding the mandible in place against the skull, observe how the mandible pivots to open and close. The muscles of mastication (which we will examine in a few days) control movement of the mandible. 

As a preview, observe how contraction of the temporalis muscle would 'pull' the mandible both upward and posteriorly due to the muscle’s attachment to the coronoid process. The masseter muscle is located on the posterolateral mandible, and spans between the mandible and the zygomatic arch. These will be examined in the deep face lab session .

On yourself at a later time, place your fingers along the margin of your mandible while clenching and unclenching your teeth and you will feel the contractions of the masseter muscle.

Observe on the inside (medial side) of the ramus of the mandible there is a large opening, the mandibular foramen. This provides access into the mandible for the inferior alveolar nerve supplying the teeth (we will examine this nerve in the deep face lab session).

At the most anterior mid-point of the mandible is the mental protuberance, also known as the chin.

14. Somatosensory innervation of the face is all derived from the trigeminal nerve (CN V) with major divisions (V1 ophthalmic, V2 maxillary, and V3 mandibular) supplying the upper, mid, and lower face via nerves emerging from small foramina on the anterior skull.
    (Netter011) (Netter013) (Photo7137)

Return to the superior orbital rim on the skull and observe a small notch or foramen in the medial region of the superior orbital rim. In most individuals this is a notch, but in some individuals the bone closes over forming a foramen.

Passing through this notch (or foramen) is the supraorbital nerve innervating most of the forehead (a branch of the CN V1 ophthalmic nerve).

Examine the inferior orbital rim for a small foramen in a line directly inferior from the superior orbital notch.

The infraorbital foramen is the emergence point for the infraorbital nerve (a branch of the CN V2 maxillary nerve) which innervates the mid-face.

Return to the mandible and examine just laterally to the mental protuberance for the mental foramen.

This foramen allows the terminal branch of the inferior alveolar nerve to emerge, where it is renamed the mental nerve innervating the chin (a branch of the CN V3 mandibular nerve).

These three foramina are typically located along an imaginary straight superior to inferior line. This line is often a guide for craniofacial reconstruction alignment.

PROCEDURE - Calvaria

15. Examine the calvaria which forms the superior part of the skull and the cranial cavity (or vault) which houses the brain.
    (Netter013) (Netter016)
    (Photo7137) (Photo7139) (Photo7140)

Frontal: The anterior part of the calvaria is formed by the frontal bone (recall the frontal eminences examined above).

Parietal: The lateral portion is formed by the left and right parietal bones.

Occipital: The posterior most portion is formed by the occipital bone. The occipital bone continues posteroinferiorly forming the posterior skull. There is a distinct bony point, the external occipital protuberance, at the posteroinferior point which serves as the attachment point for the trapezius muscle.

16. Examine the lines where the frontal and parietal bones meet and form the left and right coronal sutures.
    (Netter013) (Netter016) (Photo7139)

The lateral most point on the coronal sutures (on the side of the head) is where multiple bones converge and is called the pterion.  This is a weak point in the skull subject to fracture risk. (Photo7138a)

Deep to the pterion are branches of middle meningeal artery supplying the dura covering of the brain. Fracture of the bone here carries an elevated risk of epidural hematoma from damage to branches of the middle meningeal artery supplying the dura covering of the brain.

17. Examine the midline for the sagittal suture joining the left and right parietal bones.
    (Netter013) (Netter016) (Photo7139)

The point where the sagittal suture meets the left and right coronal sutures is called bregma and is one of the key landmarks for neurosurgery.

At birth, this intersection has not yet formed and the region is covered only by a membrane, the 'soft spot' on an infants head. This membrane covered soft spot is the anterior fontanelle, which typically closes between 15-19 months of life.

18. Examine posteriorly where the parietal bones meet the occipital bone at the left and right lambdoid sutures.
    (Netter013) (Netter016) (Photo7140)

The point where the sagittal suture meets the left and right lambdoid sutures is called Lambda and is another key landmark for neurosurgery.

The brain is mapped in a series of stereotaxic coordinates measured from bregma and lambda. This allows for precise insertion of an instrument to a specific point in the brain by using measurements from the bregma and lambda points on the skull and some 3-dimensional trigonometry.

CLINICAL EXERCISE - External Ventricular Drain

19. Interventions through the skull are performed in a craniotomy by drilling or cutting a specific point relative to bregma and lambda.

In this clinical exercise, you will perform an external ventricular drain insertion aiming to enter the lateral ventricles for treatment of hydrocephalus. 
                                   ------ click here ------>

PROCEDURE - Cranial Fossa

20. On the skull examine the floor of the cranial cavity.
    (Figure794) (Netter018) (Photo7141)

The floor of the cranial cavity is divided into an anterior cranial fossa, middle cranial fossa, and posterior cranial fossa.

The lesser wing of the sphenoid bone forms a distinct rim, marking the border between the anterior and middle cranial fossae.

The petrous part of the temporal bone has a ridge of bone which demarcates the middle cranial fossa and posterior cranial fossa.

21. Examine the anterior cranial fossa.
    (Figure701) (Netter018) (Photo7142)

The anterior cranial fossa is a depression which houses the frontal lobes of the brain.

The anterior cranial fossa is formed primarily by the orbital plates of the frontal bone and the lesser wings of the sphenoid bone. The orbital plates are directly superior to the eyeballs and form the roof of the orbit (and floor of the anterior cranial fossa).

At the midline of the anterior cranial fossa is a crest of bone, the crista galli, to which the falx cerebri dural sheet attaches. We will examine the falx cerebri in a later lab.

To each side of the crista galli is a small depression in the ethmoid bone forming the cribriform plate. The olfactory nerve (CN I) projects through small perforations in the cribriform plate (these are often too small to be visible to the naked eye).

22. Examine the middle cranial fossa.
    (Figure701) (Netter018) (Photo7142) (Photo7143)

The middle cranial fossa is a depression which houses the temporal lobes of the brain.

The middle cranial fossa is deeper than the anterior cranial fossa and starts from where the lesser wings of the sphenoid bone form the ridge between the anterior and middle cranial fossae.

The body and greater wing of the sphenoid bone form the anterior side of the fossa. The lateral, inferior, and posterior regions are all formed by parts of the temporal bone. 

At the most anterior edge of the middle cranial fossa observe the elongated superior orbital fissure between the lesser and greater wings of the sphenoid bone. You will need to tilt the skull so as to look 'under' the lesser wing of the sphenoid bone.

Most of the nerves associated with the orbit pass through the superior orbital fissure (with the exception of the optic nerve CN II which has its own canal). The cranial nerves passing through the superior orbital fissure are the oculomotor (CN III), trochlear (CN IV), the ophthalmic branch (V1) of the trigeminal (CN V) and the abducens nerve (CN VI).

Medial to the superior orbital fissure are the optic foramina through which the left and right optic nerves(CN II) pass.

The optic chiasm (crossing point for parts of the optic nerve) is at the midline just posterior to the optic foramina. In some skulls, a small depression in the bone marks the location. We will see this crossing point when we remove the brain in a later lab.

At the midline between the left and right sides of the middle cranial fossa approximately where the optic chiasm would be, find the depression in the bone forming the hypophyseal fossa.

The hypophyseal fossa is also called the sella turcica (“Turkish saddle”). This fossa holds the pituitary gland.

Just posterolateral to the superior orbital fissure is the foramen rotundum (passing the maxillary branch V2 of the trigeminal nerve CN V). The shape of the opening is roughly round, as the name implies.

Just posterolateral from the foramen rotundum is the foramen ovale (passing the mandibular branch V3 of the trigeminal nerve CN V). The shape of the opening is roughly oval, as the name implies.

Finally, just posterolateral from the foramen ovale is the foramen spinosum (passing the middle meningeal artery). Grooves for the middle meningeal artery branches extend from the foramen spinosum on the inner surface of the flat bones of the skull calvaria.

Identify the foramen lacerum located towards the medial edge of the middle cranial fossa.  In the living, cartilage seals the inferior opening of the foramen lacerum.

During the preparation of the skull, this cartilage is lost creating what appears to be a foramen which is not present in the living.

23. Examine the posterior cranial fossa.
    (Figure701) (Netter018) (Photo7142) (Photo7143)

The posterior cranial fossa is the most posterior and deepest depression and houses the brainstem and cerebellum.

The posterior cranial fossa consists anteriorly of part of the temporal bone and posteriorly the occipital bone.  

On the anterolateral aspect of the posterior cranial fossa identify the internal auditory (acoustic) meatus. The size of the internal auditory meatus varies considerably between individuals. The facial (CN VII) and  vestibulocochlear (CN VIII) nerves pass into the internal auditory meatus

At the midline in the occipital bone is the large foramen magnum, through which the spinal cord passes into the spinal canal of the vertebral column. 

Examine at the anterolateral edge of the foramen magnum for the small openings of the hypoglossal canal through which the hypoglossal nerve (CN XII) passes.

Just lateral to the hypoglossal canal is the irregular shaped jugular foramen. This is formed by a notch at the junction between the temporal bone and the occipital bone. The jugular foramen allows passage of the internal jugular vein, glossopharyngeal (IX), vagus nerve (CN X) and accessory nerve (CN XI).

PROCEDURE - skull base

24. Turn the skull over and examine the base of the skull.
    (Figure701a) (Netter017) (Photo7144)

The skull base is very complex, but we will examine only a few of the major features related to the nervous system.

25. Examine the external acoustic meatus just anterior to the mastoid process
    (Figure701a) (Netter013) (Netter017) (Photo7138)

The mastoid process is the attachment point for the sternocleidomastoid muscle.

26. Examine just anteromedial to the mastoid process a thin protrusion of bone called the styloid process.
    (Figure701a) (Netter013) (Netter017)
    (Photo7144) (Photo7145)

The styloid process is 20-25mm long but only a few millimeters in diameter. As such, it is highly fragile and many (most) of the skulls we are examining have had the styloid process snapped off over the years and only the broken stub is on most of the skulls we are examining.

27. Examine the region between the mastoid and styloid processes for a small foramen, the stylomastoid foramen.
    (Figure701a) (Netter013) (Netter017) (Photo7144)

The stylomastoid foramen is where the facial nerve (CN VII) emerges.

The facial nerve is unusual, in that it enters the skull via the internal acoustic meatus, but takes a turn inside the temporal bone to exit thorough the stylomastoid foramen.

28. Examine the skull just medial to the styloid process for the major vascular foramen.
    (Figure701a) (Netter017) (Photo7144)

Jugular foramen: The most posterior is the irregular jugular foramen through which the internal jugular vein, glossopharyngeal (IX), vagus nerve (CN X) and accessory nerve (CN XI) emerge.

If you're not sure where this is, turn the skull back over and pass a probe through the foramen from the cranial cavity side.

Carotid canal: The foramen directly anterior to the jugular foramen is the carotid canal where the internal carotid artery enters the skull. This opening is more regular and circular shaped than the jugular foramen.

Foramen spinosum: Slightly more anterior from the carotid canal is the foramen spinosum. This is the entry point for the middle meningeal artery into the skull.

The internal carotid artery is a major blood supply to the brain while the middle meningeal artery is the major blood supply to the meninges covering the brain.

29. Examine anterior and a little medial from the foramen spinosum where the foramen ovale is located.
    (Figure701a) (Netter017) (Photo7144)

If you're not sure where this is, turn the skull back over and pass a probe through the foramen ovale from the cranial cavity side.

30. When your examination of the skull is complete, return the skull to the skull box container and return the box to the tray under your table.

CLINICAL EXERCISE - Scalp Laceration

31. Minor lacerations of the skin are commonly closed using sutures, however in cases of linear lacerations skin staples are a rapid effective alternative.

In this clinical exercise, you will close your prior scalp incision using skin staples. 
                                   ------ click here ------>

32. When finished for the day, remember to check if the red bucket needs emptying, moisten any dry surfaces of the upper body with wetting agent, close up the plastic covering and clip it with hemostats, clip/zip the white bag, cover with the blue drape.

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.

Case 01

Case 02

Case 03

CHECKLIST

Skeletal Structures

Skull, anterior
    Frontal eminence
    Superior orbital rim
    Inferior orbital rim
    Nasal bones
    Zygomatic arch
    Temporal fossa
    Mandible
    Condyle process
    Coronoid process
    Supraorbital notch/foramen
    Infraorbital foramen
    Mental foramen

Skull, Calvaria
    Frontal bone
    Parietal bones
    Occipital bone
    Coronal suture
    Sagittal suture
    Bregma
    Lambda

 Superior side of the cranial base

     Anterior cranial fossa
        Crista galli
        Cribriform plate
        Optic canal
        Lesser wing of the sphenoid bone

     Middle cranial fossa
        Superior orbital fissure
        Temporal bone
        Hypophyseal fossa (sella turcica)
        Foramen rotundum
        Foramen ovale
        Foramen spinosum

     Posterior cranial fossa
        Temporal bone
        Occipital bone
        Internal auditory meatus
        Jugular foramen
        Hypoglossal canal
        Foramen magnum

 Inferior side of the cranial base
    Foramen ovale
    Foramen spinosum
    Jugular foramen
    Carotid canal
    Foramen magnum
    Stylomastoid foramen
    Mastoid process
    Styloid process 

Cranial nerves (roman numeral and foramina of exit)

I  - Olfactory— cribriform plate of the ethmoid

II - Optic — optic canal

III - Oculomotor— superior orbital fissure

IV  Trochlear— superior orbital fissure

V - Trigeminal 
    V1 - ophthalmic — superior orbital fissure
    V2 - maxillary — foramen rotundum
    V3 - mandibular — foramen ovale

VI - Abducens — superior orbital fissure

VII - Facial — internal acoustic meatus
                        (and stylomastoid foramen)

VIII - Vestibulocochlear — internal acoustic meatus

IX - Glossopharyngeal — jugular foramen

X - Vagus — jugular foramen

XI - Accessory — jugular foramen

XII - Hypoglossal — hypoglossal canal