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A coccyx with four vertebrae below the sacrum. The coccyx is formed of three, four or five rudimentary vertebrae.It articulates superiorly with the sacrum.In each of the first three segments may be traced a rudimentary body and articular and transverse processes; the last piece (sometimes the third) is a mere nodule of bone.
It stretches from median sacral crest [3] and the free margin of the sacral hiatus [1] to the dorsal surface of the coccyx. [1] The lateral sacrococcygeal ligaments run from the lower lateral angles of the sacrum to the transverse processes of the first coccygeal vertebra to complete the foramina for the last sacral nerve. [1]
The sacrum (pl.: sacra or sacrums [1]), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1–S5) between ages 18 and 30. [2] The sacrum situates at the upper, back part of the pelvic cavity, between the two wings of the pelvis. It forms joints with four other bones.
The number of vertebrae in a region can vary but overall the number remains the same. In a human spinal column, there are normally 33 vertebrae. [3] The upper 24 pre-sacral vertebrae are articulating and separated from each other by intervertebral discs, and the lower nine are fused in adults, five in the sacrum and four in the coccyx, or tailbone.
The name coccyx is derived from the Greek word for 'cuckoo' due to its beak-like appearance. The coccyx itself is made up of three to five vertebrae, some of which may be fused together. The ventral side of the coccyx is slightly concave whereas the dorsal aspect is slightly convex.
The male pelvis, formed by left and right hip bones, sacrum, and coccyx. The female pelvis is wider than the male pelvis to accommodate childbirth. At about the age of puberty, ossification takes place in each of the remaining portions, and they join with the rest of the bone between the twentieth and twenty-fifth years.
Caudal regression syndrome, or sacral agenesis (or hypoplasia of the sacrum), is a rare birth defect. It is a congenital disorder in which the fetal development of the lower spine—the caudal partition of the spine—is abnormal. [1] It occurs at a rate of approximately one per 60,000 live births. [2]
[3] [4] It is inserted by its base into the margin of the coccyx and into the side of the lowest piece of the sacrum. [3] [4] In combination with the levator ani, it forms the pelvic diaphragm. [5] The pudendal nerve runs between the coccygeus muscle and the piriformis muscle, superficial to the coccygeus muscle. [6]