The thoracolumbar fascia (lumbodorsal fascia) is a deep investing membrane which covers the deep muscles of the back of the trunk.
in the cervical region, it passes in front of the Serratus posterior superior and is continuous with a similar investing layer on the back of the neck—the nuchal fascia.
In the thoracic region the lumbodorsal fascia is a thin fibrous lamina which serves to bind down the Extensor muscles of the vertebral column and to separate them from the muscles connecting the vertebral column to the upper extremity. It contains both longitudinal and transverse fibers, and is attached, medially, to the spinous processes of the thoracic vertebrae; laterally to the angles of the ribs.
In the lumbar region the fascia (lumbar aponeurosis) was previously described as two layers, anterior and posterior. Now (in Terminoliga Anatomica) it's divided into three layers
The three layers unite at the lateral margin of the Sacrospinalis, to form the tendon of origin of the Transversus abdominis. The aponeurosis of origin of the Serratus posterior inferior and the Latissimus dorsi are intimately blended with the lumbodorsal fascia.