Osteology of the orbit

Question 1

What bones constitute the walls of the orbit?

Answer 1

1. Maxilla
2. Frontal
3. Sphenoid
4. Zygomatic
5. Palatine
6. Ethmoid
7. Lacrimal

Question 2

Where is the orbit widest?

Answer 2

Approximately 1.5cm behind the orbital margin

Question 2

How are the orbits/ orbital aperture directed?

Answer 2

Forwards, laterally and downwards
(Characteristic of primates and predators which require binocular vision)

Question 3

Dimensions and volume of orbit?

Answer 3

40mm (H) x 40mm (W) x 40mm (D)
Volume ~ 30 mL

Question 4

What bones make up the orbital roof?

Answer 4

(Orbital plate of the) Frontal bone and Lesser wing of the sphenoid

Question 5

Where is the fossa for the lacrimal gland located? (orbital roof)

Answer 5

Anterolateral aspect of the roof
Located on the inferior surface of each orbital plate of the frontal bone behind the zygomatic processes

Question 6

Where is the trochlear fossa located and what is attached there?

Answer 6

Anteromedial aspect of the roof
4mm from the margin
Site at which the trochlea is attached - tendon of the superior oblique passes through the trochlea

Question 7

Where are the anterior and posterior ethmoidal canals located and what do they transmit?

Answer 7

Junction of roof and medial wall above the
frontoethmoidal suture

They transmit the anterior and posterior ethmoidal nerves and vessels

Question 8

Relations of the orbital roof

Answer 8

Separates the orbit from the anterior cranial fossa and frontal lobes of the brain

Anteriorly, the frontal sinus lies above the orbit

The roof is thin and translucent except at the lesser wing of the sphenoid

Question 9

What bones make up the medial orbital wall?

Answer 9

1. Frontal process of the maxilla
2. Lacrimal bone
3. Orbital plate of the ethmoid
4. Body of the sphenoid

Question 10

Shape and thickness of medial wall?

Answer 10

Oblong in shape
Thin 0.2-0.4mm

Question 11

What makes up the lacrimal fossa for the lacrimal sac? (in the medial wall)

Answer 11

Smooth, more deeply concave depression on the lacrimal bone
Bound by anterior and posterior lacrimal crests and is continuous below with the nasolacrimal canal

Question 12

Which is the thinnest of the orbital walls?

Answer 12

Medial orbital wall

Question 13

What lies medial to the medial orbital wall?

Answer 13

(Anterior to posterior)
Anterior ethmoidal air cells -> middle ethmoidal air cells -> posterior ethmoidal air cells and sphenoidal sinus

Question 14

What bones make up the orbital floor?

Answer 14

1. Orbital plate of the maxilla
2. Orbital surface of the zygoma
3. Orbital process of the palatine bone

Question 15

What direction does the floor slope (from medial to lateral wall)?

Answer 15

Slopes slightly downwards from medial to lateral wall

Question 16

Path from inferior orbital fissure to outside?

Answer 16

Inferior orbital fissure -> infraorbital groove -> infraorbital canal (before it reaches the margin) -> opens as the infraorbital foramen (4mm below the orbital margin) on the anterior surface of the maxilla

Question 17

What lies inferior to the orbital floor?

Answer 17

Floor separates the orbit from the maxillary sinus

Question 18

How thick is the orbital floor?

Answer 18

0.5-1.0mm thick

Question 19

What bones make up the lateral orbital wall?

Answer 19

1. Greater wing of the sphenoid (orbital surface)
2. Zygomatic bone

Question 21

What is the Spina recti lateralis and what is its significance? (Lateral orbital wall)

Answer 21

Small bony spine on the greater wing of the sphenoid near the apex of the orbit

On the lateral orbital wall

Gives origin to part of the lateral recuts

Question 22

What is the zygomatic foramen, where is it located and what does it transmit?

Answer 22

Lateral orbital wall
Transmits the zygomatic nerve and vessels to temporal fossa and cheeks (zygomaticotemporal and zygomaticofacial nerve)