The irregular bones are bones which, from their peculiar form, cannot be groupe as long bone, short bone, flat bone or sesamoid bone. Irregular bones serve some 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). They consist of cancellous tissue enclosed within a thin layer of compact bone.