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pe·trous 'pe-trəs, 'pē- adj of, relating to, or constituting the exceptionally hard and dense portion of the human temporal bone that contains the internal auditory organs and is a pyramidal process wedged in at the base of the skull between the sphenoid and occipital bones with its lower half exposed on the surface of the skull and pierced by the external auditory canal
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pet·rous (petґrəs) [L. petrosus] resembling a rock; hard; stony.Medical dictionary. 2011.