The subarachnoid space ends at
Arachnoid & dural sheath end at the lower end of the S-2 veebra. Subarachnoid space terminates at the caudal (lower border) S-2 veebra. This is also the ending of the sub-dural space. Ref - BDC 6thedition vol 2
L1
L2
L5
S2
Abdomen and pelvis