Irregular bones serve various purposes in the body, such as protection of nervous tissue (such as the vertebrae protect the spinal cord), affording multiple anchor points for skeletal muscle attachment (as with the sacrum), and maintaining pharynx and trachea support, and tongue attachment (such as the hyoid bone).
Irregular bones can also be used for joining all parts of the spinal column together.
The spine is the place in the human body where the most irregular bones can be found.
There are, in all, 33 irregular bones found here.
Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Irregular bone.