Cranial Nerves & Skull Base › Skull Base

Inferior Skull

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Inferior Skull

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Key Definitions

Foramina are holes that allow neurovascular structures to pass through the bone.

Processes serve as muscle attachment sites.

Maxilla

Key structures of the maxilla:

  • Palatine process
    • Portion of the maxilla that extends posteriorly, towards the palatine.
  • Incisive foramen
    • A small opening for neurovascular structures; its name reflects its location posterior to the incisors (the front teeth).
    • The nasopalatine nerve and sphenopalatine artery (and vein) pass through the incisive foramen to serve the palate and associated structures.
  • Alveolar margin (aka, ridge)
    • The border of the maxilla where the upper teeth reside.

Sphenoid

Key structures of the sphenoid:

  • Pterygoid process
    • Gives rise to the medial and lateral pterygoid plates, which are extensions where muscles of mastication (aka, chewing) attach.
  • Foramen ovale
    • Petrosal nerve, mandibular nerve, and accessory meningeal artery.
  • Foramen spinosum
    • Middle meningeal artery and meningeal branch of the mandibular nerve.

Temporal bone

Key structures of the temporal bone:

  • Mandibular fossa
    • Shallow depression where the mandible (the bone of the lower jaw) articulates with the cranium.
  • External auditory meatus
    • External opening of the ear.
  • Styloid process
    • A pointy projection for attachment of muscles.
  • Mastoid process
    • Larger, roughened cone-shaped projection for muscle attachment (sternocleidomastoid).
  • Opening of the carotid canal
    • Internal carotid artery enters the cranium to supply the brain via this opening.
  • Stylomastoid foramen
    • Lies between the styloid and mastoid processes.
    • CN VII (facial nerve).

Occipital bone

Key structures of the occipital bone:

  • Foramen magnum
    • A large hole where the spinal cord enters the cranium to become the brainstem.
    • The brainstem, vertebral arteries, and CN XI (accessory nerve) pass through the foramen magnum;
  • Occipital condyles
    • Lie on either side of the foramen magnum; these rounded surfaces articulate with the vertebral column.
  • Hypoglossal canal
    • A small opening near the foramen magnum and the occipital condyles.
    • CN XII (hypoglossal nerve)
  • External occipital crest
    • Extends from the posterior edge of the foramen magnum, and terminates at the external occipital protuberance
  • External occipital protuberance
    • A roughened elevation; it serves as a muscle attachment site and is usually larger in adult males.
  • Inferior and superior nuchal lines
    • Extend horizontally from the crest; they serve as muscle attachment sites.

Additional Features

  • Foramen lacerum
    • Lies between the occipital, sphenoid, and temporal bones; it is irregularly shaped.
    • Greater petrosal nerve; it is a branch of the facial nerve (CN VII).
  • Jugular foramen - Lies between the occipital and temporal bones; it is named for the jugular vein, which exits through this space.
    • CNs IX (glossopharyngeal nerve), X (vagus), and XI (accessory), and the jugular vein