Skull Anatomy Lecture Review

The Skull: Overview and Major Divisions

• The skull is the rigid framework that protects the brain and supports the structures of the face.

• It is formed by two sets of bones:

  • Cranial bones (cranium) that enclose the brain in the cranial cavity and provide sites of attachment for head and neck muscles.

  • Facial bones that form the shape of the face and support the nasal and oral cavities.

• Key functional themes:

  • Provides attachment sites for head and neck muscles

  • Encloses brain and sensory organs

  • Contains cavities for middle and internal ear, nasal cavity, and orbits

• The skull contains a large number of openings for passageways: 85 named openings (foramina, canals, fissures) that provide passage for the spinal cord, major blood vessels, and the 12 cranial nerves. 85 named openings.

• The skull also contains paranasal sinus cavities that are mucosa-lined, air-filled spaces to warm air, lighten the skull, and assist resonance of voice.

• The skull is divided into:

  • Cranium (bones that enclose the brain)

  • Facial bones (bones of the face)

• Cavities within the skull include:

  • Middle and internal ear cavities

  • Nasal cavity

  • Orbits that house the eyeballs

• The skull is structured with several sutures (fibrous joints) that join the bones:

  • Coronal suture

  • Sagittal suture

  • Lambdoid suture

  • Squamous suture

• Fontanelles (fetal fontanelles) are unfused fibrous membranes that allow growth of the brain and ease birth. There are four fontanelles: anterior, posterior, mastoid (posterolateral), and sphenoidal (anterolateral).

• The skull is contextually organized into cranial fossae:

  • Anterior cranial fossa

  • Middle cranial fossa

  • Posterior cranial fossa

  • These fossae contribute to housing brain lobes and contain foramina for nerves and vessels; the foramen magnum is the large opening where the brain connects to the spinal cord.

  • Superior view of the cranial fossae shows spatial relationships among them.

• For orientation, the skull also houses other cavities:

  • Middle and internal ear cavities

  • Nasal cavity

  • Orbits

• The skull anatomy is commonly taught with Figures/diagrams (e.g., Figure 7.2a–c) showing cranial and facial divisions, fossae, and openings.

Cranial Bones vs. Facial Bones

• The cranium contains the following bones (grouped as a set):

  • Frontal bone

  • Parietal bones (2)

  • Temporal bones (2)

  • Occipital bone

  • Sphenoid bone

  • Ethmoid bone

• The facial bones form the anterior aspect of the skull and support the openings for the eyes, nose, and mouth. They include:

  • Zygomatic bones

  • Maxillae (upper jaw)

  • Nasal bones

  • Lacrimal bones

  • Palatine bones

  • Vomer

  • Inferior nasal conchae

  • Mandible (lower jaw) (not listed in every slide, but part of the facial skeleton)

• The skull’s structure allows the brain and sensory structures to be protected while providing muscular attachments for facial expression, mastication, and head movement.

Skull Sutures (from Term Sheets)

• Coronal suture

• Sagittal suture

• Lambdoid suture

• Squamous suture

• Sutures are fibrous joints that eventually fuse as growth completes, contributing to skull rigidity while allowing growth during development.

Paranasal Sinuses (from Term Sheets)

• The paranasal sinuses are air-filled spaces within certain skull bones:

  • Frontal sinus

  • Ethmoidal air cells (ethmoid sinuses)

  • Sphenoidal sinus

  • Maxillary sinus

• All paranasal sinuses are mucosa-lined spaces that serve several functions.

Fetal Fontanelles (from Term Sheets)

• Anterior fontanelle

• Posterior fontanelle

• Sphenoidal (anterolateral) fontanelle

• Mastoid (posterolateral) fontanelle

• Fontanelles are the unossified areas between skull bones in infants that allow brain growth and ease birth. They progressively ossify as the child matures.

The Skull (1 of 4): Bones of Cranium and Facial Divisions

• The skull is organized into two major regions with corresponding sutures:

  • Coronal suture

  • Sagittal suture

  • Lambdoid suture

  • Squamous suture

• The skull is divided into:

  • Cranial bones (that form the cranium)

  • Facial bones (that form the face)

• Figures illustrate the cranial and facial divisions and the major sutures that separate them.

Overview of Skull Geography (1 of 2)

• Facial bones form the anterior aspect of the skull; the cranium forms the remainder.

• The skull’s arrangement supports the brain and sensory organs and provides attachment points for muscles.

The Skull (2 of 4): Cranial Fossae and Foramina

• Anterior cranial fossa houses frontal lobes of the brain.

• Middle cranial fossa houses parts of the temporal lobes.

• Posterior cranial fossa houses the cerebellum.

• Foramina (openings) in the skull provide passageways for spinal cord, major blood vessels, and the 12 cranial nerves. The 12 cranial nerves are essential for sensory and motor innervation of the head and neck. 12

• Temporal lobe, frontal lobe, and cerebellum are situated relative to these fossae.

The Skull (3 of 4): Lateral View and Brain Regions

• In lateral view, the temporal lobe of the cerebrum is anterior to the cerebellum.

• The cranial fossae are arranged to accommodate the brain’s lobes and cerebellum while protecting neural tissue and supporting vascular supply.

The Skull (4 of 4): Occipital Bone and Posterior Structures

• Occipital bone forms most of the skull’s posterior wall and posterior cranial fossa.

• It articulates with the parietal, temporal, and sphenoid bones.

• Foramen magnum: the large opening through which the brain connects with the spinal cord.

• Occipital condyles flank the foramen magnum and articulate with the first cervical vertebra (C1).

• External occipital protuberance: a protrusion just superior to the foramen magnum.

• External occipital crest: ridges for ligamentum nuchae attachment.

• Superior and inferior nuchal lines: attachment sites for neck and back muscles.

The Cranium: Internal Structures and Petrous Region (Cranium 4 of 11)

• The petrous part of the temporal bone houses the middle and internal ear cavities.

• Several foramina penetrate the petrous region, including the internal acoustic meatus.

• The mastoid and styloid processes are attachment sites for several neck and tongue muscles.

• These features contribute to hearing, balance, and muscular attachments of the neck and tongue.

The Sphenoid Bone (Keystone of the Cranium)

• The sphenoid is a complex, bat-shaped bone that articulates with all other cranial bones, acting as a keystone for the cranial floor.

• It contains the sphenoidal sinuses within its body.

• The sphenoid bone includes the sella turcica and hypophyseal fossa, which enclose the pituitary gland.

The Ethmoid Bone

• The ethmoid bone is a central supporting bone of the skull, contributing to the nasal cavity and orbits.

• Key features:

  • Cribriform plate with cribriform foramina (olfactory foramina for the olfactory nerves).

  • Orbital plate (part of the orbit’s medial wall).

  • Ethmoidal air cells (ethmoidal sinuses).

  • Crista galli (superior projection for falx cerebri attachment).

  • Perpendicular plate (forms part of the nasal septum).

  • Middle nasal concha (part of the ethmoid contributing to the nasal conchae).

The Zygomatic and Other Facial Bones

• Zygomatic bones (cheekbones):

  • Form the cheek and the inferolateral margins of the orbits.

  • Articulate with the zygomatic processes of the temporal, frontal, and maxillary bones.

• Zygomatic arch:

  • Formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone.

  • Frontal process of the zygomatic bone contributes to the orbital rim.

  • Lateral margin of the orbit is associated with the zygomatic arch.

• Palatine bones: L-shaped bones formed from two bony plates; contribute to the posterior portion of the hard palate and parts of the nasal cavity.

• Vomer: Plow-shaped bone forming part of the nasal septum.

• Inferior nasal conchae: Paired bones forming part of the lateral walls of the nasal cavity; the ethmoid bone forms the other two conchae.

• Nasal bones: Form the bridge of the nose.

• Lacrimal bones: Form the medial walls of orbits; contain the lacrimal fossa for the tear drainage system (drains into the nasolacrimal canal).

• Frontal bone: Forms the forehead; includes the supraorbital margin and the optic foramen (canal).

• Nasal cavity and orbit context:

  • The orbital view lists bones contributing to the orbit: Frontal, Sphenoid, Zygomatic, Maxilla, Palatine, Lacrimal, Ethmoid.

  • The orbit is formed by seven bones; the arrangement supports the eye and its associated structures. 7 bones.

The Orbits and Nasal Cavity: Special Characteristics (1 of 3)

• Orbits encase the eyes and lacrimal glands and provide attachment sites for many eye muscles.

• Formed by parts of seven bones: Frontal, Sphenoid, Zygomatic, Maxilla, Palatine, Lacrimal, and Ethmoid.

• This multi-bone construction creates a protective, functional housing for vision-related structures.

Bones That Form the Orbits (1 of 2)

• Image/photograph of a right orbit illustrates the arrangement of the bones forming the orbit.

• The orbit’s bony walls and margins are formed by contributions from the frontal, sphenoid, zygomatic, maxillary, palatine, lacrimal, and ethmoid bones.

Paranasal Sinuses and Ethmoid Structures (continued)

• The ethmoid bone contributes to the nasal cavity and contains the cribriform plate and cribriform foramina for olfactory nerves.

• The paranasal sinuses include the frontal, maxillary, sphenoidal, and ethmoidal air cells.

The Hyoid Bone

• The hyoid bone is not a skull bone; it lies in the anterior neck, inferior to the mandible.

• It does not articulate directly with any other bone and is anchored by ligaments.

• It serves as a movable base for the tongue and as a site of attachment for swallowing muscles.

• It plays a crucial role in speech and swallowing mechanics.

Paranasal Sinuses (1 of 2) and (2 of 2)

• The frontal sinus, ethmoidal air cells, sphenoidal sinus, and maxillary sinus are shown in anterior and medial views.

• Functions of paranasal sinuses include:

  • Warming and humidifying inhaled air

  • Lightening the skull

  • Enhancing resonance of voice

Developmental Aspects of the Skeleton

• Infant skulls contain more bones than adult skulls; several bones fuse as growth occurs.

• Fontanelles connect unfused parts of the infant skull, allowing for brain growth and ease of passage through the birth canal.

• Four fontanelles exist in infants: anterior, posterior, mastoid, and sphenoidal.

• Fontanelle closure occurs as the skull bones ossify with age.

Notes on Additional Skeletal Features and Connectivity

• The skull’s articulation sites include:

  • Foramen magnum (brain-spinal cord connection)

  • Occipital condyles (articulation with atlas/C1)

  • External occipital protuberance and erect crests for neck muscle attachments

  • Mastoid and styloid processes as muscle attachment sites

• Key neurovascular passages include:

  • Optic foramen/canal in the frontal bone region

  • Internal acoustic/meatus in the temporal bone

  • Infraorbital foramen and inferior orbital fissure in the orbital region

  • Other foramina, canals, and fissures that provide passage for cranial nerves and vessels

Summary of Notable Features by Bone (Quick Reference)

• Occipital bone: posterior skull, foramen magnum, occipital condyles, external occipital protuberance, nuchal lines.

• Sphenoid bone: keystone of the cranium; sella turcica with hypophyseal fossa; sphenoidal sinuses.

• Ethmoid bone: cribiform plate with foramina, crista galli, perpendicular plate, ethmoidal air cells, orbital plate, middle nasal concha.

• Zygomatic bone and arch: cheekbone; forms part of the orbit’s lateral wall; connects with temporal and maxillary bones.

• Palatine bones: form part of the hard palate and the nasal cavity’s posterior walls.

• Vomer: nasal septum component.

• Inferior nasal conchae: lateral walls of nasal cavity; partial role of conchal bones in nasal turbulence.

• Nasal bones: bridge of the nose.

• Lacrimal bones: medial orbit walls; lacrimal fossa for tear drainage.

• Frontal bone: forehead, supraorbital margin; optic foramen.

• Orbits: formed by seven bones; optic canal, nasolacrimal canal, and related features located within or around the orbit.

Key Formulas and Notation (where applicable)

• Number of cranial nerves: 12

• Number of named openings in the skull: 85

• Number of bones contributing to the orbit: 7

• Number of fontanelles in the infant skull: 4

• Paranasal sinuses formed from bones: Frontal, Sphenoid, Ethmoid, and Maxillary (paired) — total bones contributing: 5