We now examine the articulations. Consider the rib coming out of the T4/T5 juncture. It articulates with the inferior costal facet of T4 and the superior costal facet of T5. As it arches around the back it further articulates with the transverse costal facet of T5. The thoracic vertebra articulate with each other above and below through the superior articular process, which rises above and posteriorly to the pedicle, and the inferior articular process, on the underside of the spinous process, which jets down inferiorly to meet the superior articular process. The superior vertebral notch is above the pedicle, and the inferior vertebral notch is below the pedicle. These unite to form the intervertebral foramen. From the side, the rib obscures the superior vertebral notch. The spinal nerves run through the inferior vertebral notches. Intervertebral discs are between vertebra.
Cervical vertebra differ: the spinous process is shorter and bifurcated, body is smaller, vertebral foramen is larger, there are foramen transversarium. There are no rib articulations. The articular processes are almost horizontal rather than oblique in the case of thoracic vertebra, and the inferior articular process is not located on the underside of the spinous process, but rather on the underside of the vertebra anterior to the lamina. Atlas (C1) has no body. Axis (C2) has a dens, which is the body of C1 that has become fused to C2 during development. Vertebra prominens (C7) has the most prominent spinous process, and is easily palpated on the back of the neck.
Lumbar vertebra differ. They have larger bodies, broad spinous processes that project posteriorly and do not overlap, and do not have transverse costal facets.
The sacrum consists of five fused vertebra with no identifiable spines or transverse processes. On the dorsal surface, there is a median sacral crest, four posterior sacral foramina, and a sacral hiatus. The coccyx is a small triangular bone formed by four rudimentary coccygeal vertebra.
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