What is a common origin point for both the iliocostalis and longissimus muscles?

The iliocostalis and longissimus muscles, both part of the erector spinae group, share the posterior sacrum as a common origin point. This anatomical location provides a stable base from which these muscles can extend and support the spine. The posterior sacrum, along with the spinous processes of the lumbar vertebrae and the thoracic region, serves as an anchor for these muscles, allowing them to perform their primary function of extending and laterally flexing the vertebral column.

The importance of the posterior sacrum in the function of these muscles cannot be overstated, as it facilitates not only stability during movement but also contributes to maintaining an upright posture. The other options do not relate to the origins of these specific muscles, which is why they are not correct in this context.