Anatomy of the lumbar vertebrae, sacrum and coccyx

The lumbar vertebrae have wide spines and wings. Their lower processes expand and are like guarding wings. There are five of these vertebrae. The lower back, together with the sacrum, is like the base of the entire spine. It supports and carries the pelvis, through which the nerves of the leg pass.

There are three bones of the sacrum. They are connected more firmly than all other vertebrae and have the strongest articulations. They have the widest wings, and the holes from which the nerves emerge are not at the very edges of these vertebrae, so as not to be damaged by the femoral joint, but extend significantly from the edges inward, in the forward or backward direction. The bones of the sacrum are similar to the bones of the lower back.

The coccyx is composed of three cartilaginous vertebrae that do not have processes. Their nerves grow from common openings, like those in the neck, because they are small. As for the third vertebra, a single nerve emerges from its edge.

We have said the corresponding word about the bones of the spine, but now we will say in general about the entire spine. The entire spine, as a single thing, is characterized by the best shape, that is, round. The fact is that this form is the furthest from the possibility of being damaged due to blows. Therefore, the ends of the upper vertebrae are curved downward, and the ends of the lower ones are curved upward. They connect at the middle vertebra, that is, at the tenth, and this vertebra is not curved in any direction so that both curves upward and downward can converge on it. The tenth vertebra is average in its spines, not in their number, but in length.

Since the spine must move, that is, bend and bend in both directions, this is done by bending the middle vertebra in the opposite direction, and the vertebrae above and below it bend in the desired direction, as if the ends of the spine are bending to meet. Therefore, the tenth vertebra has no bulges, but only depressions. The convexities of the overlying and underlying vertebrae face the tenth vertebra, with the overlying ones directed downwards and the underlying ones directed upwards. This makes it easier for the spine to move in the direction opposite to the tilt of the body, and allows the overlying vertebrae to bend down and the underlying vertebrae to pull up.