The rarity of reports on tumors of the filum terminale may be due to a certain extent to the neglect with which this structure is usually treated in routine necropsies. Embedded as it is in the roots of the cauda equina, small tumors of this structure, such as the one encountered in the case to be reported, may readily escape notice unless a careful examination of this portion of the spinal cord is made.
The filum terminale is the slender glistening prolongation of the end of the conus medullaris. The boundary between the cord and the filum is usually ill-defined; it may, however, be determined by a dilatation of the central canal of the spinal cord known as the ventriculus terminalis. At about the level of the second sacral vertebra the filum terminale internum (intradural filum terminale) undergoes a transition to the filum terminale externum as the dura mater becomes