Norma Lateralis

Bones Visible in Norma Lateralis

Key Anatomical Features

Sutures

• Coronal suture — between frontal and parietal bones (runs vertically)
• Sagittal suture — visible at the top (between parietal bones, seen end-on)
• Lambdoid suture — between parietal and occipital bones posteriorly
• Squamous suture — between temporal and parietal bones (arc-shaped)
• Parietomastoid suture — between parietal and mastoid part of temporal bone

Pterion

• Frontal, parietal, temporal, and sphenoid (greater wing)
• Located approximately 4 cm above the midpoint of the zygomatic arch and 3.5 cm behind the frontozygomatic suture
• It is the thinnest part of the skull
• The middle meningeal artery (anterior branch) runs in a groove on the inner surface directly beneath it
• A blow to the pterion can rupture this artery → extradural (epidural) haematoma

Temporal Fossa

• Boundaries:
  • Superior & posterior: Superior and inferior temporal lines
  • Anterior: Frontal and zygomatic bones
  • Inferior: Zygomatic arch (roof of infratemporal fossa below)
  • Medial floor: Pterion
• Contents: Temporalis muscle and its fascia, deep temporal nerves and vessels

Zygomatic Arch

• Formed by the zygomatic process of the temporal bone + temporal process of the zygomatic bone
• The masseter muscle originates from its lower border and medial surface

External Acoustic Meatus (EAM)

• Opening in the temporal bone, visible as a round foramen
• Mastoid process is posterior to it; styloid process inferior

Mastoid Process

• Posterior projection of the temporal bone
• Contains mastoid air cells communicating with the middle ear

Orbital Region

• The lateral orbital margin is formed by the zygomatic bone
• The frontozygomatic suture is visible at the lateral angle of the orbit

Mandibular Features (visible in norma lateralis)

• Coronoid process (anterior) — for temporalis attachment
• Condylar process (posterior) — forms the temporomandibular joint
• Mandibular notch between them
• Mental foramen on the body of the mandible (below 2nd premolar)

Temporal Lines

• Superior temporal line — attachment of temporal fascia
• Inferior temporal line — origin of temporalis muscle

Clinical Significance

Visual Reference

Summary of Normas (Aspects of the Skull)

Mandible

Parts of the Mandible

1. Body

• Mental protuberance — midline bony prominence forming the chin
• Mental tubercles — slight elevations on either side of the mental protuberance
• Mental foramen — oval opening midway between the upper and lower borders of the body, usually below the 2nd premolar; transmits the mental nerve and vessels (terminal branch of inferior alveolar nerve)
• Oblique line — ridge running from the anterior border of the ramus onto the external surface of the body; attachment for muscles depressing the lower lip

• Mental spines (genial spines) — two pairs of small spines posterosuperior to the symphysis
  • Superior mental spines → origin of genioglossus (tongue muscle)
  • Inferior mental spines → origin of geniohyoid muscle
• Mylohyoid line — an oblique ridge running posterosuperiorly from below the mental spines to just below the last molar; attachment for the mylohyoid muscle (floor of mouth)
• Sublingual fossa — shallow depression above the anterior ⅓ of mylohyoid line → lodges the sublingual gland
• Submandibular fossa — depression below the posterior ⅔ of mylohyoid line → lodges the submandibular gland
• Digastric fossa — at the base near midline → attachment of anterior belly of digastric

• Superior (alveolar) border — bears the alveolar arch (tooth sockets for the 16 lower teeth); resorbed when teeth are lost
• Inferior border (base) — thick and rounded; the body of the mandible measured here

2. Ramus

• Roughened in the lower part for attachment of the masseter muscle

• Mandibular foramen — large opening, the superior entrance to the mandibular canal; transmits the inferior alveolar nerve and vessels
• Lingula — a triangular bony tongue immediately anterosuperior to the mandibular foramen; attachment for the sphenomandibular ligament
• Mylohyoid groove — runs anteroinferiorly from the mandibular foramen; carries the nerve to mylohyoid
• Roughened posteroinferior area for medial pterygoid muscle attachment

Key Foramina and Canals

Muscle Attachments Summary

Temporomandibular Joint (TMJ)

• Articular surfaces covered by fibrocartilage (not hyaline cartilage)
• Divided by a fibrous articular disc into two compartments:
  • Lower compartment → hinge movement (depression/elevation)
  • Upper compartment → translatory movement (protrusion/retraction)
• Opening the mouth involves both depression and protrusion simultaneously

Ligaments of TMJ

• Lateral (temporomandibular) ligament — main ligament, thickening of joint capsule
• Sphenomandibular ligament — from spine of sphenoid to lingula
• Stylomandibular ligament — from styloid process to angle of mandible

Ossification

Diagrams

Clinical Relevance