Which of the following best describes the insertion of the iliocostalis muscle?

The iliocostalis muscle is one of the major components of the erector spinae group, which plays a crucial role in maintaining posture and allowing movement of the spine. Its primary function is to extend and laterally flex the vertebral column.

The insertion of the iliocostalis muscle is specifically at the angles of the lower ribs, which enables it to assist in rib elevation and contributes to movements of the thoracic region of the spine. This insertion point effectively supports its role in extension and lateral flexion of the trunk.

In contrast, the other choices do not accurately reflect the insertion of the iliocostalis. The superior borders of the sacrum pertain to structures involved with the pelvic region, while the medial aspect of the pecten pubis relates to the pubic bone, neither of which are locations for the iliocostalis muscle. The lower three lumbar vertebrae are part of the vertebral column but are sites pertaining to the origin of some iliocostalis fibers rather than its insertion. Thus, recognizing the specific anatomical features of the iliocostalis muscle is essential for understanding its functional mechanics.