Pelvic Girdle: Sacrum

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This bone is shaped like a triangular piece of pizza and contains little tiny holes called foramina (say it for-a MEEEEEEEN-a)

Anatomical illustration of the anterior view of the human pelvic girdle. Key structures are labeled, including the acetabulum which is outlined with a dashed line on the left side of the image, the obturator foramen, also outlined with a dashed line, and the inferior pubic ramus outlined with a dashed line on the right. Below the pelvic girdle is the text, "anterior Pelvic Girdle."
Pelvic girdle anterior view showing acetabulum, obturator foramen, and inferior pubic ramus.
  • Medial sacral crest
  • Sacral foramina

The sacrum along with the coxal or hip bones and the coccyx is part of the pelvic girdle. The pelvic girdle is where the legs attach to the body. The pectoral girdle is where the arms attach to the body.  Sometimes people will refer to the sacrum as their tailbone. However sometimes people will also refer to the coccyx as their tailbone. In all reality the coccyx or the sacrum are actually bones resulting from the fusing of vertebrae.  We can refer to the fused vertebrae by number like the other vertebrae such as S1, being the most superior.   

On the posterior face of the sacrum is the medial sacral crest.  This structure is a remnant of the spinous processes of the fused vertebrae.  Lateral to the median sacral crest are these lines of little holes called foramina.  These holes are where nerves and arteries penetrate the sacrum and are officially called the sacral foramina.  

Illustration of the anterior side of the sacrum and coccyx along with the posterior side of the full pelvic girdle. Key parts are labeled, including the sacral foramina on the anterior side and the median sacral crest on the posterior side. These anatomical structures are shown in a light-yellow color, set against a plain white background.
Anterior sacrum with coccyx and posterior full pelvic girdle with key features labeled.

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