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

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