A Human Skull with a Tripartite Inca Bone: A Case Report

Abstract

An adult human skull was discovered in a college osteological collection presenting with two Inca bones. Inca bones or interparietal (supernumerary) bones are rarely seen among dry human skulls. Their frequency of presentation is much less than that of sutural or Wormian bones. Inca bones or interparietal (supernumerary) bones are accepted as normal variants most often found in the occipitoparietal region of the skull. Their characteristic shape, a triangle, resembles a monument design of the Inca tribe of South America and Latin America. The significance of the presence of these variants is that Inca bones or interparietal bones may be mistaken for a skull fracture. They may also be very useful in forensic identification of an unknown individual.

A Study on the Incidence and Morphometry of Interparietal Bone in Adult Human Skulls

“…The highest percentage of 10% was noted in the West African population with the Japanese being next highest at 4.4%. (9) The geographical and ethnographical pattern of incidence of Inca bones shows a definite topographical and racial predilection and thus a possible genetic inheritance. Pedigree studies showed that the Inca bone is inherited as dominant trait with 50% penetrance and suggested genetic background for occurrence of Inca bone.…”