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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 joint locks (or rather becomes close packed) on one side as weight is transferred from one leg to the other, and through the pelvis the body weight is transmitted from the sacrum to the hip bone. The motions of the sacroiliac joint Anterior innominate tilt of both hip bones on the sacrum (where the left and right move as a unit)
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 posterior border of the ala of sacrum, shorter than the anterior, also presents two projections separated by a notch, the posterior superior iliac spine and the posterior inferior iliac spine. The posterior superior iliac spine serves for the attachment of the oblique portion of the posterior sacroiliac ligaments and the multifidus.
The appendicular skeleton, comprising the arms and legs, including the shoulder and pelvic girdles, contains 126 bones, bringing the total for the entire skeleton to 206 bones. Infants are born with about 270 bones [ 4 ] with most of it being cartilage, but will later fuse together and decrease over time to 206 bones.
3D medical animation still shot of human skull. The axial skeleton is the core part of the endoskeleton made of the bones of the head and trunk of vertebrates.In the human skeleton, it consists of 80 bones and is composed of the skull (28 bones, including the cranium, mandible and the middle ear ossicles), the vertebral column (26 bones, including vertebrae, sacrum and coccyx), the rib cage ...
The body is composed of cancellous bone, which is the spongy type of osseous tissue, whose microanatomy has been specifically studied within the pedicle bones. [4] This cancellous bone is in turn, covered by a thin coating of cortical bone (or compact bone), the hard and dense type of osseous tissue. The vertebral arch and processes have ...
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]