Falx

from The Collaborative International Dictionary of English v.0.48

Falx \Falx\, n. [L., a sickle.] (Anat.)
   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.
   [1913 Webster]