Skull Bone Classification Quiz

Skull Bone Classification

• Skull bones are divided into two categories: facial bones (14 bones) and cranial bones (8 bones).
• Facial bones form the facial skeleton.
• Cranial bones form the cranial cavity, also known as the braincase.

Facial Bones

• The facial skeleton comprises the following bones:
  • Zygomatic bones (2): form the cheekbones
  • Maxillae (2): form the upper jaw
  • Nasal bones (2): form the bridge of the nose
  • Lacrimal bones (2): form the medial wall of the orbit
  • Vomer (1): forms the lower part of the nasal septum
  • Palatine bones (2): form the posterior part of the hard palate
  • Inferior conchae (2): form the lateral walls of the nasal cavity
  • Mandible (1): forms the lower jaw

Cranial Bones

• The cranial cavity consists of the following bones:
  • Frontal bone (1): forms the forehead and anterior part of the cranial vault
  • Parietal bones (2): form the sides and roof of the cranial vault
  • Occipital bone (1): forms the posterior part of the cranial vault and base of the skull
  • Temporal bones (2): form the sides of the skull and house the organs of hearing and balance
  • Sphenoid bone (1): forms part of the base of the skull, the orbit, and the middle cranial fossa
  • Ethmoid bone (1): forms part of the roof of the nasal cavity, the orbit, and the cribriform plate

Cranial Cavity Structure

• The cranial cavity is composed of two main parts:
  • Vault (calvaria): forms the roof and side walls of the cranial cavity
  • Cranial base: forms the floor of the cranial cavity
• The vault is composed of two layers of compact bone separated by a layer of spongy bone called diploe (contains red marrow).

Functions of the Skull

• Encloses and protects the brain.
• Forms the skeleton of the upper parts of the alimentary and respiratory systems.
• Provides protection for the organs of sight, hearing, and smell.
• Is intimately related to the teeth and soft tissues of the oral region.

Anterior View of the Skull

• Bones seen in the anterior view: frontal bone, maxillary bones, zygomatic bones, nasal bone, mandible, nasal bones, vomer, inferior concha, zygoma.
• Landmarks:
  • Orbital apertures and anterior nasal aperture (piriform aperture)
  • Supraorbital margin formed by the frontal bone
  • Superciliary arch, a smooth elevation above the supraorbital margin, forms the eyebrow ridge
  • Glabella, a slight elevated area above the bridge of the nose
  • Supraorbital notch or foramen in the superior orbital margin
  • Infraorbital foramen in the lower margin of the orbit
  • Mental foramen in the mandible below the apices of the premolars
  • Nasal bones form the bridge of the nose
  • Anterior nasal aperture formed by the nasal bones and maxillae
  • The nasal septum divides the nasal cavity
  • Zygomatic bone forms the prominence of the cheek

Superior View of the Skull

• Bones seen in the superior view: frontal bone, parietal bones, occipital bone.
• Landmarks:
  • Sagittal suture between the two parietal bones
  • Coronal suture between the frontal and parietal bones
  • Lambdoid suture between the occipital and parietal bones
  • Parietal foramen on the posterior part of the parietal bone
  • Frontal (metopic) suture, a median suture in immature skulls that usually fuses during childhood
  • Bregma, the junction of the coronal and sagittal sutures, corresponding to the anterior fontanelle on the fetal skull
  • Lambda, the junction of the lambdoid and sagittal sutures, corresponding to the posterior fontanelle on the fetal skull

Lateral View of the Skull

• Bones seen in the lateral view: frontal bone, parietal bones, occipital bone, temporal bone, sphenoid bone, zygoma, maxilla, lacrimal bone, nasal bone, mandible.
• Landmarks:
  • Temporal lines (superior and inferior)
  • Temporal fossa, an area on the lateral wall of the skull
  • Infratemporal fossa located below the temporal fossa
  • Pterion, an H-shaped suture where the frontal, sphenoid, parietal, and temporal bones meet, crossed internally by the middle meningeal artery and vein
  • Temporomandibular joint (TMJ)
  • External acoustic meatus, a bony canal leading to the middle ear
  • Mastoid process, a bony prominence behind the external acoustic meatus
  • Styloid process, a long, slender process projecting downwards from the temporal bone
  • Zygomatic arch, a bony arch formed by the articulation of the temporal and zygomatic bones

Clinical Significance of Pterion

• Trauma to the pterion can lead to tearing of the middle meningeal vessels, which lie between the dura mater and the periosteum of the skull.
• This can cause a build-up of blood, resulting in:
  • Compression of the brain tissue
  • Decrease in level of consciousness
  • Untreated hemorrhage may cause death in a few hours.