Using a skull, identify the labeled features shown in the above images.

Review these images of a disarticulated skull.

Review these images of a fetal skull. Note anterior fontanelle and choanae.

Make an incision from the mastoid process along the jawline to the nasolabial fold. Continue the incision superiorly lateral to the mouth, nose and orbit to the brow. Incise from the brow to one cm above the external ear.

Reflect the flap posteriorly. Make this flap superficial to avoid facial muscles.

Identify the margins of the parotid gland. Locate the parotid duct extending anteriorly superficial to the masseter muscle.

Locate the temporal, zygomatic, buccal, mandibular and cervical branches of the facial nerve.

Along the anterior margin of the parotid, follow the plane of the parotid duct into the parotid gland. This plane divides the gland into superficial and deep lobes. The branches of facial nerve (VII) lie in this plane. This dissection is technically difficult.

Try to identify the trunk of the nerve near the stylomastoid foramen and follow the temporofacial and cervicofacial divisions.

The main branches of the facial nerve are temporal, zygomatic, buccal, mandibular and cervical.

Anterior to the facial nerve, identify the retromandibular vein and the external carotid artery.

Reflect the scalp using a bicoronal incision across the top of head from ear to ear.  You may need to make anterior and posterior midline incisions to reflect the scalp to the orbital rim and occiput.

Using an oscillating saw, make a circumferential cut (Figure 5.1a) through the skull from just superior to the orbits to the external occipital protuberance. The temporalis muscle may be sharply incised at the level planned for the bone cuts or cut through this muscle with the oscillating saw.

If not previously performed with spine dissection, make lateral occipital bone cuts that extend to the foramen magnum after sharply dissecting occipital and cervical musculature away from the occipital bone (5.1b).

Elevate the skull cap to expose the brain and dura mater.  Dissect the dura free from the skull where possible.

Make vertical cuts at the lateral and medial borders of the orbit to separate the superior orbital rim (5.1c-e).  Elevate the orbital rim and orbital roof to expose the contents of the orbit. This orbitofrontal craniotomy may be carried out at this point or following brain removal when examining the skull base and orbit.

In the following steps, gradually expose the base of the brain and skull to examine cranial nerves and vasculature. Begin by gently elevating the frontal lobes to expose anterior structures. Locate the following structures:

• Olfactory bulbs
• Optic nerves (II)
• Optic chiasm
• Carotid arteries
• Tips of temporal lobes

Extra illumination will be helpful.

Continue gentle retraction of the frontal lobes for further exposure of the base of brain. Sharply divide the optic nerves and internal carotid arteries to examine more posterior structures.  Identify the:

• Sella turcica
• Infundibulum
• Oculomotor nerves (III)

Continue to expose the ventral surface of the brain and interior of the skull base.

Identify the basilar artery on the ventral surface of the pons and midbrain.

Locate the superior cerebellar and posterior cerebral arteries. Locate the oculomotor nerve between these two arteries.

Re-identify the optic nerves and chiasm and the internal carotid arteries.

Divide the tentorium along the petrous (temporal) ridge to prepare to expose and free the cerebellum and brainstem. Also, divide the tentorium posteriorly with the donor prone or lateral.

With the tentorium reflected identify the:

• Trochlear (IV)
• Trigeminal (V)
• Abducens (VI)
• Facial (VII)
• Auditory (VIII)
• Glossopharyngeal (IX)
• Vagus (X)
• Accessory (XI)
• Hypoglossal (XII)

The trochlear nerve will be difficult to see with this view.

Locate the formation of the basilar artery from the union of the right and left vertebral arteries.

To remove the brain and spinal cord as a unit, first divide the remaining intact cranial nerves and vertebral arteries. With the donor lateral, elevate the brain from the skull base along with the spinal cord from the spinal canal.

The spinal cord or spinal cord with surrounding dura should be elevated. Depending on which of these approaches is chosen, nerve roots will need to be cut intra or extra-durally.

Set the brain and spinal cord aside for further examination.