General features.-The lumbar vertebrae (figs. 276-278, five in number, can be distinguished from the other vertebrae by their great size and by the absence of costal facets on the sides of the bodies.
The body is large, wider from side to side than from before backwards, and a little deeper in front than behind. The vertebral foramen is triangular in shape, larger than in the thoracic region but smaller than in the cervical region. The shape is accounted for by the shortness of the pedicles and the direction of the laminar, which pass backwards as well as medially. The spine projects almost horizontally backwards, is somewhat quadrangular, and is thickened along its posterior and inferior borders. The superior articular processes bear articular facets which look medially and backwards and are gently concave .The posterior borders of the process is marked by a rough elevation, termed the mamillary process. The inferior articular processes bear articular facets which are slightly convex and are directed laterally and forwards. Transverse processes are thin and elongated, with the exception of those of the fifth lumbar vertebra, which are strong and substantial. A small, rough elevation marks the postero-inferior aspect of the root of the transverse process and is termed the accessory process.
The fifth lumbar vertebra (fig. 278) can be distinguished by the fact that its body is usually deeper in front than behind, a condition which is associated with the prominence of the sacro-vertebral angle. In addition, the strong transverse process is connected to the whole of the lateral aspect of the pedicle and encroaches on to the side of the body.
Particular features.–The upper and lower borders of the bodies in front and behind give attachment to the anterior and posterior longitudinal ligaments. Lateral to the anterior longitudinal ligament, the bodies of the upper lumbar vertebra; (three on the right side; two on the left) give origin to the crura of the diaphragm. Postorolateral to the cars the psoas major arises from the bodies of all the lumbar vertebrae. These muscles throw tendinous arches across the side of the bodies to protect the lumbar vessels. The vertebral foramen of the first lumbar vertebra contains the lower end of the spinal cord (coitus medullaris); the lower foramina contain the cauda egnina and the spinal meninges. The pedicle is strong and springs from the posterolateral aspect of the body just below its upper border. The superior vertebral notch, though shallow is easily recognizable: the inferior notch is of considerable depth. The laminae are broad short and strong, but they do not overlap one another as they do in the thoracic region. They give attachment to the ligament flava. The spines provide attachment for the posterior lamella of the lumbar fascia the sacrospinalis. The spine thoracis, the multifidus the interspinal muscles and ligaments and the supraspinous ligaments. The spine of the fifth lumbar vertebrae is the least, substantial and its extremity is more. or less rounded and down-turned. The superior articular process are wider apart than the inferior in the upper lumbar region, bit the difference is very slight in the fourth and in the fifth the two measurements are approximately equal, The articular as the other harts of the lumbar vertebra. They increase in length from the first to the third, which is the longest of all the transverse facets arc so shaped that. while they permit of flexion and extension, they prevent rotation of the lumbar vertebrae. The transverse processes, with the exception of the fifth, are not so strongly as the other parts of the lumbar vertebrae. They increase in length from the first to the third, which is the longest of all transverse processes, and then become shorter. A faint, vertical ridge marks the: anterior surface of the transverse process nearer the tip than the root. It gives attachment to the anterior later of the lumbar fascia and separates the surface into a medial area. for the attachment of the psoas major, and a lateral area for the quadratus lumborum.. The tip of the process gives attachment to the middle layer of the lumbar fascia, but, in addition, the tip of the. first gives attachment to the medial and lateral arcuate ligaments (lumboscostal arches) and the tip of the fifth to the iliolumbar ligament. The posterior surfaces of the, transverse processes are covered by the deep muscles of the back and give origin to fibers of the longissimus thoracis (longissimus dorsi) muscle. The upper and lower borders of the process give attachment to lateral intertransverse muscles. The mamillary process is homologous with the superior tubercle in the twelfth thoracic vertebra. It gives attachment to the multifidus and to the medial intertransverse muscle. The accessory process varies in prominence and may be difficult to identify. It gives attachment to the medial intertransverse muscle. The costal element is incorporated in the transverse process (fig. 113).