Bones of the Orbit

Overview

• Base (orbital rim) opening anteriorly onto the face
• Apex directed posteromedially (at the optic foramen)
• 4 walls: roof, floor, medial, lateral

Orbital Rim (Base)

• Superiorly: Frontal bone
• Medially: Frontal process of the maxilla
• Inferiorly: Zygomatic process of the maxilla + zygomatic bone
• Laterally: Zygomatic bone + frontal process of the zygoma + zygomatic process of the frontal bone

Wall-by-Wall Detail

Roof (Superior Wall)

• Main bone: Orbital part of the frontal bone
• Posterior completion: Lesser wing of the sphenoid bone
• Key markings:
  • Trochlear fovea (anteromedially): attachment pit for the pulley (trochlea) of the superior oblique muscle
  • Lacrimal fossa (anterolaterally): lodges the orbital part of the lacrimal gland
  • May contain part of the frontal sinus anteriorly

Medial Wall

• Bones (anterior to posterior): Frontal process of maxilla → Lacrimal bone → Ethmoid bone (lamina papyracea) → small part of Sphenoid
• The ethmoid bone (lamina papyracea) is the largest contributor
• Key markings:
  • Lacrimal groove: formed between the lacrimal bone (posterior lacrimal crest) and the frontal process of the maxilla (anterior lacrimal crest); contains the lacrimal sac
  • Anterior ethmoidal foramen: at the frontoethmoidal suture; transmits the anterior ethmoidal nerve and vessels
  • Posterior ethmoidal foramen: slightly posterior; transmits posterior ethmoidal nerve and vessels

Floor (Inferior Wall)

• Also forms the roof of the maxillary sinus
• Main bone: Orbital surface of the maxilla
• Small contributions: Zygomatic bone (anterolateral) and orbital process of the palatine bone (posteromedial corner)
• Key markings:
  • Inferior orbital fissure: runs along the lateral boundary of the floor; bounded by greater wing of sphenoid, orbital surface of maxilla, and orbital process of palatine bone
  • Transmits: infraorbital nerve (CN V2 branch), zygomatic nerve, branches of the sphenopalatine ganglion, infraorbital artery and vein, ophthalmic vein branch

Lateral Wall

• Anterior: Zygomatic bone
• Posterior: Greater wing of the sphenoid bone
• Key markings:
  • Superior orbital fissure: between the greater wing (below) and lesser wing (above) of the sphenoid; transmits CN III, IV, V1, VI, superior ophthalmic vein, orbital branch of middle meningeal artery, recurrent lacrimal artery branch
  • The lateral wall is the thickest and strongest wall

Key Foramina / Apertures at the Apex

Clinical Correlates

• Orbital blow-out fractures most commonly involve the floor (thinnest bone, roof of maxillary sinus) and medial wall (lamina papyracea of ethmoid). Floor fractures can trap the inferior oblique muscle causing vertical diplopia (upward gaze failure).
• Medial wall fractures allow air into the orbit from the ethmoidal sinuses - seen on X-ray as orbital emphysema; patients may feel orbital fullness when blowing the nose.
• Superior orbital fissure syndrome: compression of structures here causes ophthalmoplegia, ptosis, fixed dilated pupil (CN III, IV, VI involvement) - WITHOUT visual loss.
• Orbital apex syndrome: involves the optic canal too, so adds vision loss to the above findings.

Location of the Palatine Bone in the Orbit

Exact Position

         MEDIAL WALL
              |
Ethmoid ------+-------- Sphenoid (lesser wing)
              |
         PALATINE  <-- sits HERE, at this 3-way junction
              |
       Maxilla (floor) ---- Zygoma

• Wall: Floor (inferior wall)
• Position on floor: Posterior + medial corner
• Neighbors: Maxilla (anteriorly), ethmoid (medially), sphenoid (posteriorly)

Also Contributes to the Inferior Orbital Fissure

• Greater wing of sphenoid
• Orbital surface of maxilla

Why It Matters Clinically