Norma Lateralis - Lateral View of the Skull

What Is It?

Bones Visible in Norma Lateralis

Sutures

• Coronal suture - runs vertically between the frontal bone (anteriorly) and the parietal bone (posteriorly)
• Sagittal suture - (seen end-on) runs along the top of the skull
• Lambdoid suture - curves posteriorly between the parietal bone (anteriorly) and the occipital bone (posteriorly)
• Squamous suture - the curved suture between the temporal bone and the parietal bone
• Parietomastoid suture - between the parietal and mastoid part of the temporal bone
• Occipitomastoid suture - between the occipital bone and the mastoid part of the temporal bone
• Temporozygomatic suture - between the temporal and zygomatic bones (forming the zygomatic arch)
• Frontozygomatic suture - between the frontal and zygomatic bones at the lateral orbital margin

Key Bony Landmarks

1. Temporal Lines

• The superior temporal line arches across the parietal bone and serves as the upper limit of the temporal fossa. The temporalis fascia attaches here.
• The inferior temporal line is the attachment line for the temporalis muscle.

2. Pterion

• The most important landmark in norma lateralis.
• An H-shaped sutural region where four bones meet: frontal, parietal, greater wing of sphenoid, and temporal bones.
• Located 4 cm above the midpoint of the zygomatic arch and 2.5 cm behind the frontozygomatic suture.
• Clinically critical: the thinnest part of the skull. Deep to it lies:
  • The anterior division of the middle meningeal artery
  • The middle meningeal vein
  • The stem of the lateral sulcus (Sylvian point) of the brain
• A blow to the pterion can rupture the middle meningeal artery, causing an extradural (epidural) haematoma.

3. Asterion

• The point where three sutures meet posteriorly: lambdoid, parietomastoid, and occipitomastoid sutures.
• In infants, this is the site of the posterolateral (mastoid) fontanelle, which closes by about 12 months of age.

4. Zygomatic Arch

• A bony bridge formed by:
  • The zygomatic process of the temporal bone (posteriorly)
  • The temporal process of the zygomatic bone (anteriorly)
• Joined at the temporozygomatic suture.
• The masseter muscle arises from the lower border and medial surface of the zygomatic arch.

5. Mastoid Process

• A conical downward projection of the mastoid part of the temporal bone, posterior to the external acoustic meatus.
• Contains mastoid air cells (pneumatized in adults).
• Site of attachment for the sternocleidomastoid, splenius capitis, and longissimus capitis muscles.

6. Styloid Process

• A slender, needle-like projection from the inferior surface of the temporal bone, anteromedial to the mastoid process.
• Directed downwards, forwards, and slightly medially.
• Its base is partly ensheathed by the tympanic plate; its apex is usually hidden behind the posterior border of the mandibular ramus.
• Gives attachment to the stylohyoid, styloglossus, and stylopharyngeus muscles and the stylohyoid and stylomandibular ligaments (the "styloid bouquet").

7. External Acoustic Meatus (EAM)

• The opening into the ear canal.
• Bounded anteriorly by the mandibular fossa and posteriorly by the mastoid process.

8. Mandibular Fossa & Articular Tubercle

• The mandibular fossa is a concavity in the temporal bone that receives the condylar head of the mandible.
• The articular tubercle lies anterior to the fossa; the condyle slides forward onto it during mouth opening.
• Together they form the temporomandibular joint (TMJ).

Fossae Visible in Norma Lateralis

Temporal Fossa

• Boundaries:
  • Above: superior temporal line
  • Below (lateral): upper border of zygomatic arch
  • Below (medial): infratemporal crest of greater wing of sphenoid
  • Anterior wall: zygomatic bone, frontal bone, and sphenoid bone (separates fossa from orbit)
  • Floor: formed by parts of frontal, parietal, temporal, and greater wing of sphenoid - crossed at the pterion by an H-shaped suture
• Contains the temporalis muscle and the zygomaticotemporal foramen (on the temporal surface of the zygomatic bone in the anterior wall).

Infratemporal Fossa

• Irregular space below the zygomatic arch, not directly visible in the norma lateralis but its opening is seen when the zygomatic arch is followed inferiorly.
• Boundaries:
  • Anterior: posterior surface of the body of the maxilla
  • Roof: infratemporal surface of the greater wing of sphenoid
  • Medial: lateral pterygoid plate
  • Lateral: ramus of the mandible
• Contains: lateral and medial pterygoid muscles, maxillary artery, mandibular nerve (V3) branches, chorda tympani, and pterygoid venous plexus.

Mandible in Norma Lateralis

• Body - horizontal part bearing the lower teeth
• Ramus - vertical part; its superior end divides into:
  • Coronoid process (anterior) - for temporalis muscle attachment
  • Condylar process (posterior) - head articulates at the TMJ
• Mandibular notch - between coronoid and condylar processes
• Angle of mandible - junction of body and ramus; site of masseter attachment laterally and medial pterygoid medially
• Mental foramen - on the lateral surface of the body, below the 2nd premolar; transmits the mental nerve and vessels (branch of inferior alveolar nerve/artery)

Clinical Relevance Summary