Where does the iliocostalis lumborum insert?

• A. Spinous processes of lumbar vertebrae.
• B. Mastoid process.
• C. Iliac crest.
• D. Angles of the lower ribs (7-12) and the transverse processes of the lumbar vertebrae.

Answer: (D)

Iliocostalis lumborum attaches to the angles of the lower ribs (typically ribs 7–12) and to the transverse processes of the lumbar vertebrae. This position fits its role as the lateral part of the erector spinae, which runs from the pelvis up the back to the ribs and vertebrae. When it contracts, it helps extend the spine and, if contracting on one side, laterally flexes the trunk. The muscle also has its origin along the iliac crest and nearby thoracolumbar fascia, from which it fibers upward to those rib and lumbar attachments. The other options don’t match: spinous processes are attachment sites for other back muscles, the mastoid process is for some neck muscles, and the iliac crest is generally an origin site rather than an insertion for this muscle.