Irregular bone

The irregular bones are bones that from their peculiar form, cannot be grouped as long bone, short bone, flat bone or sesamoid bone. 
Irregular bones serve some special purpose in the body: 
(1) protection of nervous tissue (such as the vertebrae protect the spinal cord), 
(2) 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).
The irregular bones are: the vertebræ, sacrum, coccyx, temporal, sphenoid, ethmoid, zygomatic, maxilla, mandible, palatine, inferior nasal concha, and hyoid.