The obex is the most caudal point within the fourth ventricle, as it narrows and communicates with the central canal of the spinal cord. It is one of four routes via which cerebrospinal fluid may flow from the fourth ventricle (the others being the median and two lateral apertures).

The obex occurs at the level of the foramen magnum. Therefore, it also represents the level which distinguishes the intracranial medulla and the extracranial spinal cord.

History and etymology

"Obex" is Latin for "barrier".

Anatomy: Brain

Anatomy: Brain

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Article information

rID: 5851
Section: Anatomy
Synonyms or Alternate Spellings:

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