What is a curved fold or process of the dura mater or the peritoneum; esp., one of the partitionlike folds of the dura mater which extend into the great fissures of the brain called?

falx — A curved fold or process of the dura mater or the peritoneum; esp., one of the partitionlike folds of the dura mater which extend into the great fissures of the brain. (Webster's 1913.)