D501-Lab 27

Cranial Fossae

Grant's Dissector 158-168

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Today's Goals:

1. Remove the skull cap (calvarium) and the brain
2. Explore the cranial fossae and identify its important structures

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Dissection Notes

Removal of the calvarium: Remove the scalp. Draw a line around the skull ½ inch above the superior orbital margins and the external occipital protuberance. Carefully saw through the skull until the calvarium is free from all bony attachments. Do not saw into the brain. Pry off the calvarium. In D501 we will NOT remove a wedge of occipital bone. Your lab instructor will (help) carry out the actual removal of the brain. There will not be any brain tags in the gross anatomy laboratory practical exam.

Meninges of Brain (remember the spinal cord? same thing here)

• Dura mater, outer tough membrane consisting of 2 indistinguishable layers except where they separate to enclose venous sinuses (see below)
• Arachnoid, between dura mater and pia mater, note the arachnoid granulations
• Pia mater, closely applied to the brain

Venous Sinuses (Dis. P. 167 Fig. 7.28; Dis. P. 162 Fig. 7.24; Net. Pl. 103 & 104)

• superior sagittal, upper border of the falx cerebri; usually continuous with the right transverse sinus
• right and left transverse sinuses
• inferior sagittal sinus, lower margin of falx cerebri
• straight sinus, inferior sagittal sinus and great cerebral vein
• confluens, posterior cranial fossa
• sigmoid sinus, posterior cranial fossa, direct continuations of the transverse sinus
• superior petrosal, middle cranial fossa
• cavernous sinus, middle cranial fossa

Folds of Dura Mater (Dis. P. 162 Fig. 7.23; Net. Pl. 103 & 104)

• falx cerebri, divides the 2 cerebral hemispheres
• falx cerebelli, divides the 2-cerebellar hemispheres
• tentorium cerebelli, separates the cerebellar lobe & the occipital pole of the cerebral hemispheres

The Cranial Fossae (Dis. P. 165 Fig. 7.27; Net. Pl. 9; Net. Pl. 10)

Identify the fossae & the cranial nerves. (Dis. P. 167 Fig. 7.28)

Anterior Cranial Fossa

• Sphenoid Bone
• Ethmoid Bone
• crista galli, attachment for falx cerebri
• cribriform plate (CN I-olfactory bulbs)
• Frontal Bone, roof of orbital cavities

Middle Cranial Fossa
Identify the trigeminal nerve and the three major divisions (V₁ V₂ V₃) of C.N. V.

• superior orbital fissure (CNs III, IV, V₁, VI, sympathetic fibers & superior ophthalmic vein)
• Foramen Rotundum (CN V₂)
• Foramen Ovale (V₃, lesser petrosal nerve, accessory meningeal artery)
• Foramen Spinosum (middle meningeal artery)

The middle meningeal artery and its branches are of great clinical importance. The anterior branch of the middle meningeal artery crosses the area of the pterion.

Q1. What is the pterion?

Also identify the following in the middle cranial fossa:

• trigeminal ganglion, 3 divisions of CN V (V₁, V₂, V₃) (Dis. P. 167 Fig. 7.28)
• cavernous sinus (Dis. P. 167 Fig. 7.29)

Posterior Cranial Fossa

• foramen magnum, look for the spinal portion of CN XI and the vertebral arteries
• hypoglossal canal (CN XII)
• jugular foramen (CNs IX, X & XI & sigmoid sinus-IJV)
• internal acoustic meatus (CNs VII & VIII)

ANS 1. The pterion is the thinnest part of the lateral wall of the skull, where the frontal, sphenoid, temporal and parietal bones are all close together. The pterion overlies the anterior branch of the middle meningeal artery;