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Because of evolution, I know that the human anatomy is comprised of a few vestigial elements, and the tailbone (coccyx) is listed among one of them.

  1. But doesn't the tailbone still serve a present function? Like aren't muscles and such attached to it? And doesn't it help our posture when sitting? Or does "vestigial" mean we don't use it for the same purposes as our earlier ancestors? Or how is it classified?
  2. I've heard that a few people have actually been born with the tailbone appendages -- is this accurate? I suspect that they were surgically removed when the baby was born. What is the name for when someone is born with the actual tailbone appendage?
  3. Also, is the condition of spina bifida the condition were the fetus started to grow a tail, but it never fully developed?
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1. You are right, the coccyx is the remnant of a vestigial tail, but still not entirely useless.

According to eMedicine, it is an important attachment for various muscles, tendons and ligaments—which makes it necessary for physicians and patients to pay special attention to these attachments when considering surgical removal of the coccyx. Additionally, it is also a part of the weight-bearing tripod structure which acts as a support for a sitting person. When a person sits leaning forward, the ischial tuberosities and inferior rami of the ischium take most of the weight, but as the sitting person leans backward, more weight is transferred to the coccyx.

2. It's not actually accurate for a child to be born with a tailbone appendage. The dorsal cutaneous appendage, or so-called human tail is a rare congenital anomaly with a prominent lesion from the lumbosacrococcygeal region. It is also often considered to be a cutaneous marker of underlying occult dysraphism. You are right again, there has been a report of a 9 - month old healthy male infant brought for consultation for a “tail like” structure in the lumbosacral area since birth.

3. No, it isn't. Spina bifida is a condition where the spine does not develop properly, leaving a gap in the spine. The spine consists of the spinal column, which is a solid structure made up of bones (called vertebral bodies) separated by discs of fibrous tissue. Behind this is an enclosed space called the spinal canal, which contains the spinal cord. The spinal cord connects all the nerves in the body to the brain. The canal is surrounded by arches of bone attached to the backs of the vertebral bodies.

In cases of spina bifida, something goes wrong and the arches of bone do not fully close. Sometimes there is only a gap in the bony arch, but at other times the spinal cord is also involved and does not form properly either. The skin over the arch can also either be intact or have a gap as well.

For more info on spina bifida, visit this site.

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    this was extremely informative and I really appreciated all the time and effort you took to answer these. You cleared up a lot of my misconceptions! Thank you so much!! – Butterfly and Bones Feb 4 '17 at 8:09

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