Place the donor in prone position. Identify the anterior, middle and posterior fossae (Fig. 1.1a).

In the anterior fossa, note the cribriform plate, branches of olfactory nerve (I) and the bulge of orbital plate of the frontal bone (Fig. 1.1b).

In the parasellar region, note the infundibulum in midline, optic nerves (II), internal carotid artery, oculomotor nerve (III) and trochlear nerve (IV) (Fig. 1.1c).

In the posterior fossa, note the trigeminal nerve (V) just behind the line of tentorium. Below it and slightly medial is the abducens nerve (VI). The facial (VII) and auditory nerves (VIII) are further caudal and lateral with an exit point at the internal acoustic meatus. The cranial nerves IX, X and XI, glossopharyngeal, vagus and accessory, are inferior to VII and VIII with an exit point at the jugular foramen (Fig. 2a).

At foramen magnum, identify spinal cord and vertebral arteries. Laterally, locate spinal root of accessory nerve (XI) and hypoglossal nerve (XII) (Fig 2b).

In the middle cranial fossa, note the middle meningeal artery coursing through dura. Reflect the dura to show the impression of this artery in skull. Note the entry point of the middle meningeal artery into the dura at the foramen spinosum.

Question 1: What can be the consequence of traumatic disruption of middle meningeal artery?

Examine the base of brain in relation to the skull base.

Note the frontal and temporal lobes, brainstem and cerebellum. Note the olfactory bulb and tract. Note the optic nerve, optic chiasm and optic tract and adjacent internal carotid artery. Note the oculomotor nerve (III) arising between the posterior cerebral and superior cerebellar arteries coursing medial to the temporal lobe. The trochlear nerve (IV) may be difficult to identify.

Examine the circle of Willis. Identify the internal carotid artery. Locate its middle and anterior cerebral branches. Identify the vertebral and basilar arteries. Locate the posterior cerebral and superior cerebellar branches of the basilar artery.

Identify the anterior communicating artery connecting the anterior cerebral arteries and the posterior communicating arteries connecting the posterior cerebral and internal carotid arteries.

Note individuals have considerable variation in the configuration of circle of Willis. Examine other donors.

Examine the region of the pons and medulla.

On the lateral pons, identify the trigeminal (V) nerve.

At the pontomedullary junction, locate the abducens (VI) nerve medially and the facial (VII) and auditory (VIII) nerves laterally.

On the lateral medulla, locate the bulge of the inferior olive. Posterior to the olive, locate strands of glossopharyngeal (IX), vagus (X) and accessory (XI) nerves. Anterior to the olive, between the olive and pyramid, locate strands of hypoglossal (XII) nerve.

Return to the skull base.

Orient by locating the trigeminal (V) nerve at the skull base. Remove the dura overlying the entry point of V nerve into dura. Sharply dissect this dura to expose the V nerve (semilunar ganglion) and branches of the V nerve: ophthalmic (V1), maxillary (V2) and mandibular (V3).

Extend sharp dural dissection medially to expose the cavernous sinus. Within the cavernous sinus, identify the oculomotor (III) and trochlear (IV) nerves.

Re-identify the optic nerve, internal carotid artery and infundibulum medial to the cavernous sinus.

Reflect the oculomotor nerve (III) medially and ophthalmic branch (V1) laterally to locate the internal carotid artery and abducens nerve (VI) within the cavernous sinus.

Question 2: Estimate the distance from the cavernous carotid artery to the pituitary gland.

If not previously performed, make vertical cuts at the lateral and medial borders of the orbit to separate the superior orbital rim.  Elevate the orbital rim and orbital roof to expose contents of the orbit.

Remove the remaining bone of the orbital roof covering the superior orbit including exposure of the optic canal. Open periorbital fascia.

Identify in the superior orbit:

• Levator palpebrae superioris
• Superior rectus
• Medial rectus
• Lateral rectus
• Superior oblique
• Lacrimal gland

Note the pulley arrangement of the superior oblique.

Also try to locate the lacrimal, frontal and nasociliary branches of the ophthalmic nerve (V1) and the trochlear (IV) and abducens (VI) nerves. There will be numerous small arteries and veins which make these nerves difficult to locate.

Separate the levator palpebrae superioris and superior rectus to identify the globe and optic nerve. Inject the globe with one to two cc of hyaluronic acid to restore turgor.

Divide the optic nerve and muscles close to the globe. Remove the eyeball for dissection.

Follow the steps in Dr. Forster’s video below, Anatomy of the Eye, to dissect the globe.