Anatomy of the cranial base

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Anatomy of the cranial base

USMLE® Step 1 questions

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Figure 1: Anatomy of the cranial base, inferior view
Figure 2: Anatomy of the hard palate and bony nasal septum, A. inferior view, and B. parasagittal view.
Figure 3: Anatomy of the sphenoid bone, A. superior, B. inferior, and C. anterior views.
Figure 4: Interior of the cranial base, superior view


USMLE® Step 1 style questions USMLE

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A 39-year-old man is involved in a motor vehicle collision. A CT scan of the head is performed and reveals the following:

Image reproduced from Radiopedia

The vessel that is most likely ruptured in this patient enters the skull via which of the following structures? 


The cranial base is the most inferior part of the skull.

It consists of the floor of the cranial cavity plus the inferior aspect of the viscerocranium, minus the mandible.

Together with the cranial vault, which is the part of the skull that protects the brain, it contributes to the neurocranium.

Now, the cranial base is a highly irregular surface from both an external and internal view.

So let’s begin with the external surface of the cranial base, which is formed by the maxillary, palatine, vomer, sphenoid, and occipital bones, in the midline; and the zygomatic and temporal bones laterally.

In the most anterior part of the cranial base, there are the alveolar arch and the hard palate.

The hard palate makes up both the roof of the mouth and the floor of the nasal cavity, and it’s made up of the palatine processes of both maxil lary bones and the horizontal plates of both palatine bones behind them.

The maxillary teeth border the hard palate anteriorly and on both sides.

Right behind the incisor teeth there’s the incisive fossa, which has one or more incisive foramina, that allow the nasopalatine nerves and the terminal branches of the sphenopalatine arteries to pass through.

Posteriorly and laterally, on the horizontal plate of each palatine bone, there’s the greater palatine foramen; and right behind it, the lesser palatine foramen through which the greater and lesser palatine nerves and arteries emerge.

Now, superior to the posterior end of the hard palate are the posterior nasal apertures - or choanae - which are also bounded by the body of the sphenoid bones superiorly, the medial pterygoid plates laterally, and the vomer medially.

The choanae allow air to pass from the nasal cavities into the pharynx.


  1. "Netter's Atlas of Neuroscience" Elsevier (2021)
  2. "Snell's Clinical Neuroanatomy" LWW (2018)
  3. "Moore's Clinically Oriented Anatomy" LWW (2022)
  4. "Cranial Nerves" undefined (2005)
  5. "Principles of Anatomy and Physiology" Wiley (2019)

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