The iliocostalis originates from the sacrum, erector spinae muscle aponeurosis and iliac crest. The iliocostalis has three different insertions according to the parts:

iliocostalis lumborum has the lumbar part(where its insertion is in the 12th to 7th ribs)

iliocostalis thoracis where its insertion runs from the last 6 ribs to the first 6 ribs.

iliocostalis cervicis which runs from the first 6 ribs to the posterior tubercle of the transverse process of C6-C4.