A&P Chapter 9: The Skull - Cranial Bones

The Skull: Cranial Bones

Overview of the Skull

  • The skull is composed of:
    • Cranial Bones (8)
    • Facial Bones (14)
    • Middle Ear Bones (6)

Cranial Bones

  • The cranial bones form the cranial cavity and house/protect the brain.

List of Cranial Bones

  • Frontal Bone
  • Parietal Bones (2)
  • Temporal Bones (2)
  • Occipital Bone
  • Sphenoid Bone
  • Ethmoid Bone

Details About Each Cranial Bone

Frontal Bone

  • Key Structures:
    • Supraorbital Margins: Help form the superior orbit; structurally reinforce the face.
    • Coronal Suture: Joint between the frontal bone and the parietal bones.
    • Frontal Sinus: Cavity within the frontal bone, lined by mucus-producing pseudostratified columnar epithelium.

Parietal Bone

  • Key Structures:
    • Sagittal Suture: Joint between the left and right parietal bones.
    • Coronal Suture: Also the joint between the frontal bone and the parietal bones.
    • Lambdoid Suture: Joint between the parietal bones and the occipital bone.

Occipital Bone

  • Key Structures:
    • Lambdoid Suture: Joint between the parietal bones and the occipital bone.
    • External Occipital Protuberance: A bump serving as an attachment point for an important ligament and for the trapezius muscle.
    • Foramen Magnum: A hole connecting the cranial and vertebral cavities; allows the spinal cord to connect to the brainstem.
    • Occipital Condyles: Projections that articulate with the superior articular facets of the atlas (the first cervical vertebra).

Temporal Bone

  • Key Structures:
    • Squamous Suture: Joint between the parietal bone and the temporal bone.
    • Squamous Part: Thin semicircular region near the squamous suture.
    • External Auditory Meatus: Inward extending passageway through the temporal bone; the bony portion of the external ear canal.
    • Mastoid Process: Large projection posterior to the external auditory meatus; serves as an attachment site for several muscles, including the sternocleidomastoid.
    • Styloid Process: Slender projection inferior to the external auditory meatus; an attachment site for several tongue and throat muscles.
    • Zygomatic Process: Long projection anterior to the external auditory meatus; articulates with the temporal process of the zygomatic bone, forming the posterior portion of the zygomatic arch.
    • Mandibular Fossa: Indentation that articulates with the condyle of the mandible to form the temporomandibular joint.
    • Petrous Part: Ridgelike eminence visible in the cranial cavity that houses the structures of the middle and inner ear.

Ethmoid Bone

  • Key Structures:
    • Cribriform Plate: A flat region in the anterior cranial floor surrounded by the frontal bone and containing numerous holes known as olfactory foramina, which allow the passage of olfactory nerves from the nasal cavity to the brain.
    • Crista Galli: A projection extending superiorly from the cribriform plate, acting as an anchor point for the cranial meninges.
    • Orbital Plate: Forms part of the medial wall of the orbital cavity, alongside the sphenoid, palatine, maxillary, and lacrimal bones.
    • Perpendicular Plate: A thin process extending inferiorly from the body of the ethmoid bone, forming the superior portion of the bony nasal septum.
    • Superior and Middle Nasal Conchae: Projections lateral to the perpendicular plate, lined by mucus-secreting pseudostratified columnar epithelium, which increase the turbulence of nasal airflow.
    • Ethmoid Sinus: A group of cavities within the ethmoid bone, lined by mucus-producing pseudostratified columnar epithelium.

Sphenoid Bone

  • Key Structures:
    • Sella Turcica: A concavity in the body of the sphenoid bone, where the pituitary gland rests.
    • Greater Wing: Paired processes extending laterally and curving upward on each side of the sella turcica, forming part of the floor of the cranial cavity and the posterior walls of the orbital cavities.
    • Lesser Wing: Flat shelf-like structure anterior to the sella turcica, also contributing to the floor of the cranial cavity and forming part of the posterior walls of the orbital cavities.
    • Optic Canal: Extends through the lesser wing, connecting the orbital cavity to the cranial cavity, allowing the passage of the optic nerve and the ophthalmic artery.
    • Sphenoid Sinus: A cavity within the body of the sphenoid bone, lined by mucus-producing pseudostratified columnar epithelium.
    • Pterygoid Processes: Inferior projections of the sphenoid bone that serve as attachment points for chewing muscles, positioned relative to the upper jaw.