Flat Bones are
broad, flat plates whose function is to protect soft organs and tissues.
The surface of the bones are also used as attachment for muscles.
Examples include the top and side part of the skull, sternum, shoulder
blades, and ribs.
Irregular Bones or
mixed bones have no definite shape. The function of irregular bones is
dependent on the bone. For example in the skull, the lower jaw structure
is irregular with no other counterpart on the rest of the skeleton.
Other examples include the sacrum and spinal column.