Is it farther or further?
"tough outer membrane surrounding the brain," c.1400, from Medieval Latin dura mater cerebri, literally "hard mother of the brain," a loan-translation of Arabic umm al-dimagh as-safiqa, literally "thick mother of the brain." "In Arabic, the words 'father,' 'mother,' and 'son' are often used to denote relationships between things" [Klein].
dura mater dura ma·ter (mā'tər, mä-)
The tough fibrous membrane covering the brain and the spinal cord and lining the inner surface of the skull. Also called dura , pachymeninx.