[TA] enlargement of the subarachnoid space between the conus medullaris of spinal cord (about vertebral level L2) and inferior end of subarachnoid space and dura mater (about vertebral level S2); occupied by the posterior and anterior roots constituting the cauda equina, the terminal filum, and cerebrospinal fluid; site for lumbar puncture and spinal anesthesia. SYN: cisterna lumbalis [TA].