The os incae.

The The os incae is an integral feature of reptilian and various mammalian skulls which demonstrate intramembranous ossification centers behind the parietal bones. In man, the interparietal portion of the occipital squamosa arises in membrane from a single ossific focus. Normally it fuses with the supraoccipital segment of the occipital squamosa. Occasionally there are multiple ossification centers in the interparietal bone which fail to fuse, resulting in one of several varieties of os incae.