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The sacral promontory    is the anterior lip of the superior base of the sacrum. Lateral to this is the roughened auricular surface, which joins with the ilium portion of the hipbone to form the immobile sacroiliac joints of the pelvis. Passing inferiorly through the sacrum is a bony tunnel called the sacral canal    , which terminates at the sacral hiatus    near the inferior tip of the sacrum. The anterior and posterior surfaces of the sacrum have a series of paired openings called sacral foramina    (singular = foramen) that connect to the sacral canal. Each of these openings is called a posterior (dorsal) sacral foramen    or anterior (ventral) sacral foramen    . These openings allow for the anterior and posterior branches of the sacral spinal nerves to exit the sacrum. The superior articular process of the sacrum    , one of which is found on either side of the superior opening of the sacral canal, articulates with the inferior articular processes from the L5 vertebra.

The coccyx, or tailbone, is derived from the fusion of four very small coccygeal vertebrae (see [link] ). It articulates with the inferior tip of the sacrum. It is not weight bearing in the standing position, but may receive some body weight when sitting.

Sacrum and coccyx

This figure shows the structure of the sacrum and coccyx. The left panel shows the vertebral column with the sacrum and coccyx highlighted in pink. The middle panel shows the anterior view and the right panel shows the posterior view of the sacrum and coccyx.
The sacrum is formed from the fusion of five sacral vertebrae, whose lines of fusion are indicated by the transverse ridges. The fused spinous processes form the median sacral crest, while the lateral sacral crest arises from the fused transverse processes. The coccyx is formed by the fusion of four small coccygeal vertebrae.

Intervertebral discs and ligaments of the vertebral column

The bodies of adjacent vertebrae are strongly anchored to each other by an intervertebral disc. This structure provides padding between the bones during weight bearing, and because it can change shape, also allows for movement between the vertebrae. Although the total amount of movement available between any two adjacent vertebrae is small, when these movements are summed together along the entire length of the vertebral column, large body movements can be produced. Ligaments that extend along the length of the vertebral column also contribute to its overall support and stability.

Intervertebral disc

An intervertebral disc    is a fibrocartilaginous pad that fills the gap between adjacent vertebral bodies (see [link] ). Each disc is anchored to the bodies of its adjacent vertebrae, thus strongly uniting these. The discs also provide padding between vertebrae during weight bearing. Because of this, intervertebral discs are thin in the cervical region and thickest in the lumbar region, which carries the most body weight. In total, the intervertebral discs account for approximately 25 percent of your body height between the top of the pelvis and the base of the skull. Intervertebral discs are also flexible and can change shape to allow for movements of the vertebral column.

Each intervertebral disc consists of two parts. The anulus fibrosus    is the tough, fibrous outer layer of the disc. It forms a circle (anulus = “ring” or “circle”) and is firmly anchored to the outer margins of the adjacent vertebral bodies. Inside is the nucleus pulposus    , consisting of a softer, more gel-like material. It has a high water content that serves to resist compression and thus is important for weight bearing. With increasing age, the water content of the nucleus pulposus gradually declines. This causes the disc to become thinner, decreasing total body height somewhat, and reduces the flexibility and range of motion of the disc, making bending more difficult.

Questions & Answers

what is thymus?
Jakia Reply
The thymus is a specialized primary lymphoid organ of the immune system.  thymus is located in the upper front part of the chest, in the anterior superior mediastinum, behind the sternum, and in front of the heart.
Analyn
if you are shot with a bullet and it penetrate your lung, which thoracic body cavity will be affected, and which layer of serous membrane would damage first?
Mnm Reply
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Abila
heart and cell membrane
Romantic
Anterior thoracic body cavity will be affected and parietal layer of serous membrane will he damaged.
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Romantic
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Ishwar
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Romantic
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Francis Reply
I think it is related to the digestive system. if it is then it is a way of saying that every task is done in a systematic way.
Mitali
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Samuel
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Charles
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Rita Reply
206
Hussain
300
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300
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Vineeta
300
irshad
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abul Reply
What's the pathophysiology of Coronary heart disease
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AYOMIDE Reply
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Ateeq
the protrusion of a loop or knuckle of an organ or tissue through an abnormal opening
Hussein
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the lower part of the rectum that cannot develop hence mutated
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Luba
femur
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Fatima Reply
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Johna
the study of the human body structure and how the parts are organised.
Charles Reply
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Josefs
Structure of human body?
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levels of organization of the human body
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ATIM
the smallest cell in body
what is the function of stomach?
Bilal
the sperm is smallest cell in body
asma
anatomical description of human heart
Luceno Reply
what is human heart in anatomical perspective?
Luceno
Heart is a hollow muscular organ situated in the between the lungs in a space called mediastinum
Rukayya
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Esther
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Esther
different between primary and secondary healing
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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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