The lumbar triangle actually consists of two different triangles: (1) the superficial inferior lumbar triangle (or Petit triangle) and (2) the deep superior lumbar triangle (or Grynfeltt-Lesshaft triangle). Don't ask us what forms the borders of these triangles; we don't remember that sh*t.
Did You Know
If you are unsuccessful with a lumbar puncture, you can always consider inserting the spinal needle into the left or right lumbar triangles. We're not saying it'll work, just that you can consider doing it.