Lecture 12 - Osteology of the Skull

Question 1

What are the two methods of bone formation in the skull and where are bones of each type found?

RL12 S41

Answer 1

Endochondral:
-underlie floor of skull

Dermal:
-wall and roof of skull

Question 2

What are the components of the chondrocranium?

RL12 S41

Answer 2

Neurocranium:

• forms beneath the brain
• consists of olfactory, optic, and otic portions

Splanchnocranium:
-gill arches (mandible is first gill arch)

Question 3

What are notable characteristics of the ethmoid bone?

RL12 S42

Answer 3

Only bone formed entirely in cartilage.

Components:

• cribiform plate (holes for olfactory nerves)
• crista galli (attachment for flax cerebri)

Question 4

What are notable characteristics of the sphenoid bone?

RL12 S43-44

Answer 4

Components:
-hypophyseal fossa (sella turcica)
-greater wing (lower flap)
—foramen rotundum: CN-V2
—foramen ovale: CN-V3
—foramen spinosum: blood vessels
-lesser wing (upper flaps)
—optic canal

Question 5

What are notable characteristics of the temporal bone?

RL12 S45

Answer 5

Petrous part:
-dense portion around ear apparatus

Squamous part:
-lateral wall of braincase

Tympanic part:
-bone around ear drum

Mastoid process:
-air-filled and easily infected

Styloid process:

• derived from second gill arch
• muscle attachment

Question 6

What are notable characteristics of the occipital bone?

RL12 S46

Answer 6

Foramen magnum:
-passage of spinal cord, vertebral arteries, and spinal root

Nuchal lines:
-palpable

Question 7

What are the cranial fossae and their contents?

RL12 S50

Answer 7

Anterior fossa:

• formed by frontal bone
• cribiform plate and olfactory foramina
• contains frontal lobes

Middle fossa:

• formed by sphenoid bone
• foramen rotundum (CN-V2)
• foramen ovale (CN-V3)
• foramen spinosum (middle meningeal vessels)
• foramen lacerum (nothing)
• contains temporal lobe

Posterior:

• formed by occipital bone
• foramen magnum
• jugular foramen
• cilvus
• tentorium incisure
• contains cerebellum, pons, and medulla