The Cranial Floor

• The cranial floor (aka ‘skull base’) is made up of 7 bones
  • Frontal (paired)
  • Ethmoid
  • Sphenoid
  • Temporal (paired)
    • Can  consider the squamous (pink) and petrous (purple) parts separately
  • Occipital

    

Cranial Fossae

• The skull base can be subdivided into 3 regions (aka Cranial Fossae)

• The fossae are named from anterior to posterior
  • They also ‘descend‘ from superior to inferior. This is illustrated below
• 

  Simplified schematic of the positions of the cranial fossae.

1. Anterior cranial fossa
   • From the frontal sinus to the sphenoid sinus (specifically anterior clinoid processes and planum sphenoidale)
   • Contains frontal bone
   • Contains the olfactory nerve and bulb (cribiform plate)
2. Middle cranial fossa
   • From the anterior aspect of the petrous part of temporal bone to the clivus (formed from the occipital/sphenoid bones)
     • Laterally to the lateral limit of the sphenoid /petrous
     • (i.e. the whole middle fossa is lesser sphenoid bone + petrous temporal bone)
   • Contents
     • Contains pituitary gland and temporal lobe
     • Also contains many foramina (from optic canal to IAM)
3. Posterior cranial fossa
   • From the clivus to the occipital bone
     • Essentially made up of occipital bone + some contribution from the sphenoid/temporal
   • Contents
     • Cerebellum and brainstem
     • Vertebral arteries + posterior Circle of willis