The External Skull

Describe the anatomical division of the skull into Neurocranium and Viscerocranium.

Neurocranium

• Bony case enclosing the brain, meninges, proximal cranial nerves and cerebral vasculature

• Superior portion “calvaria” - consists of mostly flat bones

• Floor “basicranium'“ - composed of irregular bones

Viscerocranium

• Facial skeleton

• Maxilla provides sockets for upper teeth

• Mandible (only moveable skull bone) provides sockets for lower teeth

• Mandible articulates with cranial base at TMJ

Describe the bony walls of the orbit, listing which bones contribute to each wall.

Roof: F-L “Flying Low”

• Frontal and Lesser wing of sphenoid

Lateral Wall: Z-G “Zero Gravity”

• Zygomatic and Greater wing of sphenoid

Medial Wall: M-L-E-S “My Little Eyes See”

• Maxilla, Lacrimal, Ethmoid, Sphenoid (body)

Floor: M-Z-P “My Zesty Pizza”

• Maxilla, Zygomatic, Palatine

List the 4 major foramina visible on the facial aspect of the skull, stating the bone each lies in and the structures transmitted.

Three of these sit in a perfect line passing through the pupil. Just follow the CN V divisions from top to bottom:

Foramen

1. Supraorbital (above eye)

Bone

• Frontal

Trigeminal Division

• V1 (ophthalmic)

Foramen

2. Infraorbital (below eye)

Bone

• Maxilla

Trigeminal Division

• V2 (maxillary)

Foramen

3. Mental (on chin)

Bone

• Mandible

Trigeminal division

• V3 (mandibular)

The Zygomaticofacial Foramen is the only one off to the side

• Bone: Zygomatic

• Structures Transmitted: Zygomaticofacial Nerve, Artery and Vein

• Nerve Origin: Branch of V2 (same as Infraorbital)

A patient presents with numbness of the cheek below the orbit following a midface fracture. Which foramen is likely involved and which nerve is injured?

• Injury Site: Infraorbital Foramen (located in the maxilla), just below the eye socket)

• Nerve Involved: Infraorbital Nerve

• Nerve Origin: A terminal branch of the Maxillary Nerve (V2) which is the second division of the Trigeminal Nerve (CN V)

• Sensory Distribution:

• Lower eyelid

• Lateral nose

• Cheek (below the orbit)

• Upper lip

Describe the Temporal Fossa.

The Temporal Fossa

• Shape: Fan-shaped depression on the lateral skull

• Primary Occupant: Temporalis Muscle (a major muscle of mastication)

The “Box” Boundaries

• Superior and Posterior: Superior temporal line

• Inferior: Zygomatic arch

• Anterior: Frontal bone and Zygomatic bone

• Lateral: Temporal fascia

• Medial: The pterion (where the frontal, parietal, temporal and sphenoid bones meet)

Describe the Infratemporal Fossa.

Where is it?

• Medial to: Jawbone (Ramus of the Mandible)

• Deep to: Cheekbone (Zygomatic Arch)

What’s inside? (The “3 M’s”)

1. Muscles: The Lateral and Medial Pterygoids and the bottom of the Temporalis

2. Mandibular Nerve (V3): The nerve that gives sensation to lower teeth and chin

3. Maxillary Artery: The main artery supplying blood to the face and teeth

How do things get in?

• The Ceiling: Foramen Ovale (hole where the V3 nerve drops down from the brain)

• The Side Door: Pterygomaxillary Fissure