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 posterior layer is attached to the spinous processes of the lumbar and sacral vertebrae and to the supraspinal ligament;
- The middle layer (previously anterior layer) is attached,medially, to the tips of the transverse processes of the lumbar vertebrae and to the intertransverse ligaments, below, to the iliolumbar ligament, and above, to the lumbocostal ligament.
- The anterior layer, the Fascia Covering the Quadratus Lumborum, is a thin layer attached,medially, to the bases of the transverse processes of the lumbar vertebrae; below, to the iliolumbar ligament; above, to the apex and lower border of the last rib. The upper margin of this fascia, which extends from the transverse process of the first lumbar vertebra to the apex and lower border of the last rib, constitutes the lateral lumbocostal arch. Laterally, it blends with the lumbodorsal fascia, the anterior layer of which intervenes between the Quadratus lumborum and the Sacrospinalis.
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.
This definition incorporates text from a public domain edition of Gray's Anatomy (20th U.S. edition of Gray's Anatomy of the Human Body, published in 1918 – from http://www.bartleby.com/107/).