cranial fossa cranial fossa a cranial fossa is formed by the floor of the cranial cavity. cranial fossathree cranial fossae and its boundaries. purple: anterior cranial fossa blue: middle cranial fossa green: posterior cranial fossa boundaries 1: sphenoidal limbus (anterior margin of the chiasmatic groove) 2: posterior borders of the lesser wings of the sphenoid 3: dorsum sellae of the sphenoid bone 4: superior borders of the petrous part of the temporal bone 5: groove for transverse sinus of the occipital boneidentifiersfma321144anatomical terminology there are three distinct cranial fossae: anterior cranial fossa (fossa cranii anterior), housing the projecting frontal lobes of the brain middle cranial fossa (fossa cranii media), separated from the posterior fossa by the clivus and the petrous crest housing the temporal lobe posterior cranial fossa (fossa cranii posterior), between the foramen magnum and tentorium cerebelli, containing the brainstem and cerebellum additional images animation. illustration. superior view and lateral view.