the sacral vertebrae, and think it's 4 to 5 that are fused together
The vetebrae of the lower back are called lumbar vertebrae. Lower than that, the vertebrae are fused together in the sacrum, and the lowest part of the spine is the tailbone or coccyx.
In type I, all of the cervical and upper thoracic vertebrae are fused together into one block. In type II, one or two pairs of cervical vertebrae are fused together. In type III, there is lower thoracic or lumbar fusion
The five vertebrae that are fused within the pelvic bones are the sacral vertebrae, as well as a few vestigal caudal vertebrae that are called the coccyx in humans.
There are normally 33 vertebrae in infant humans. There are five that will be fused as they become adults to form the sacrum and four that will be fused into coccygeal bones (tail).
No, the coccyx is smaller. The coccyx is formed by fused vertebrae.
sacrum and coccyx
There are 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, the 5 sacral vertebrae fused to form the sacrum, and the 4 coccygeal vertebrae fused to form the coccyx. Depending on the way you count the number of bones, it comes to as few as 26 bones (just the fused sacrum and fused coccyx are counted) or 33 bones (if you count each bone that is fused).
Almost all humans are born with 33 separate vertebrae. By adulthood, most have only 24. This is due to the fusion of the vertebrae in certain parts of the spine during normal development. Different textbooks give different answers to this question. The confusion comes from the fact that the two lowest vertebrae -- the sacrum and the coccyx -- are each one bone, but they are made up from smaller bones fused together. There are 24 separate vertebrae; then there is the sacrum, which is formed from 5 fused vertebrae; and finally the coccyx, which is formed from between 3-5 fused vertebrae. Therefore, if the coccyx and sacrum are each classed as one vertebra, then there are 26 vertebrae. If the fused vertebrae are all counted separately, then there are 32-34 vertebrae.
The vertebral column is made of 7 cervical, 12 thoracic, and 5 lumbar vertebrae. Additionally the sacrum, or tailbone, consists of 5 vertebrae that are wholly or partially fused together.
Despite the amusing name, Ankylosing Spondylitis is a serious medical condition. It can can cause the vertebrae to become fused together, making the spine rigid.
You tend to think about the sacrum. But it is not the case. You have the tail bone or the coccyx. It is the most inferior bone in the vertebral column.