Study Notes: Skull Bones – Cranial, Facial, and Orbital Anatomy

Skull Bones

I. Cranial Bones

The cranial bones form the protective case around the brain and provide attachment points for head and neck muscles. They are classified into several distinct bones, each with unique anatomical features and landmarks.

• Frontal Bone

  • Supraorbital margin: The superior rim of the eye socket, providing protection for the eye.

  • Glabella: The smooth area between the eyebrows, above the nasal bones.

• Parietal Bones

  • Coronal suture: The joint between the frontal and parietal bones.

  • Sagittal suture: The joint between the two parietal bones, running along the midline of the skull.

  • Lambdoid suture: The joint between the parietal bones and the occipital bone.

  • Squamous suture: The joint between the parietal and temporal bones.

• Occipital Bone

  • External Occipital Protuberance: A prominent projection on the posterior aspect of the occipital bone, palpable at the back of the head.

  • Occipital condyles: Rounded projections that articulate with the first cervical vertebra (atlas), allowing nodding movements of the head.

  • Foramen magnum: The large opening at the base of the skull through which the spinal cord passes.

  • Hypoglossal canal: Passage for the hypoglossal nerve (cranial nerve XII).

• Temporal Bones

  • Squamous Region:

    • Zygomatic process: Forms part of the cheekbone.

    • Mandibular fossa: Depression that articulates with the mandible (jaw bone).

  • Tympanic Region:

    • External auditory meatus: Canal leading to the eardrum and middle ear.

    • Styloid process: Slender pointed projection for muscle attachment.

  • Mastoid Region:

    • Mastoid process: Prominent bone behind the ear for muscle attachment.

  • Petrous Region:

    • Jugular canal: Passage for the jugular vein.

    • Carotid canal: Passage for the internal carotid artery.

• Sphenoid Bone

  • Sella turcica: Saddle-shaped depression that houses the pituitary gland.

  • Greater/lesser wings: Lateral extensions that contribute to the floor of the cranium.

  • Optic canal: Passage for the optic nerve (cranial nerve II).

  • Pterygoid processes: Projections for muscle attachment.

• Ethmoid Bone

  • Superior/Middle nasal conchae: Thin, scroll-like bones that increase surface area in the nasal cavity.

  • Perpendicular plate: Forms part of the nasal septum.

  • Crista Galli: Vertical projection for attachment of the brain's meninges.

II. Facial Bones

The facial bones shape the face, form the cavities for the sense organs, and provide openings for air and food passage. They also anchor the teeth and facial muscles.

• Mandible

  • Body: The horizontal portion containing the lower teeth.

  • Ramus: The vertical extension on each side.

  • Condylar process: Articulates with the temporal bone to form the temporomandibular joint.

  • Mandibular foramen: Opening on the inner surface for nerves and vessels.

  • Mental foramen: Opening on the anterior surface for nerves and vessels.

  • Alveolar margin: Ridge containing the tooth sockets.

• Maxilla

  • Frontal process: Extension toward the frontal bone.

  • Alveolar margin: Ridge containing the upper tooth sockets.

  • Palatine process: Forms the anterior part of the hard palate.

• Zygomatic Bones

  • Temporal process: Articulates with the temporal bone to form the zygomatic arch.

• Nasal bones: Form the bridge of the nose.

• Lacrimal bones: Small bones forming part of the medial wall of each orbit; contain the lacrimal fossa for tear drainage.

• Palatine bone: Forms the posterior part of the hard palate and part of the nasal cavity.

• Vomer: Forms the inferior part of the nasal septum.

• Inferior nasal concha: Thin, curved bones in the nasal cavity that help filter and humidify air.

III. Orbital Cavity

The orbital cavity houses the eye and associated structures. It is formed by contributions from several cranial and facial bones, providing protection and passageways for nerves and vessels.

• Optic foramen: Opening for the optic nerve and ophthalmic artery.

• Superior orbital fissure: Slit-like opening for cranial nerves and vessels.

• Inferior orbital fissure: Passage for nerves and vessels to the face.

Summary Table: Major Skull Bones and Key Features

Bone	Key Features	Function/Significance
Frontal	Supraorbital margin, Glabella	Forehead, upper orbit protection
Parietal	Coronal, Sagittal, Lambdoid, Squamous sutures	Form sides and roof of cranium
Occipital	External Occipital Protuberance, Occipital condyles, Foramen magnum	Posterior skull, spinal cord passage
Temporal	Zygomatic process, Mandibular fossa, Mastoid process, Styloid process	Side of skull, jaw articulation, muscle attachment
Sphenoid	Sella turcica, Greater/lesser wings, Optic canal	Central skull base, pituitary gland housing
Ethmoid	Superior/Middle nasal conchae, Crista Galli, Perpendicular plate	Nasal cavity structure, septum formation
Mandible	Body, Ramus, Condyle, Mental/Mandibular foramen	Lower jaw, teeth support, chewing
Maxilla	Frontal process, Alveolar margin, Palatine process	Upper jaw, hard palate formation
Zygomatic	Temporal process	Cheekbone, zygomatic arch
Nasal	Bridge of nose	Nasal structure
Lacrimal	Lacrimal fossa	Tear drainage
Palatine	Posterior hard palate	Palate, nasal cavity
Vomer	Inferior nasal septum	Divides nasal cavity
Inferior nasal concha	Curved bone in nasal cavity	Air filtration, humidification

Additional info:

• The skull consists of 22 bones: 8 cranial and 14 facial bones.

• Sutures are immovable joints that fuse cranial bones together.

• Foramina and canals in the skull allow passage of nerves and blood vessels essential for sensory and motor functions.