Indian Journal of Forensic Medicine & Toxicology

Os Inca, also known as interparietal bones, are supernumerary bones found in the interparietal region of the occipital bone, adjacent to the lambdoid suture. They are found due to incomplete fusion of the ossification centres of the interparietal region of the squamous part of occipital bone. In the present case, two such additional ovoid bones were seen in the skull, immediately to the right of the apex of the occipital squamosa, intervening between the occipital and the right parietal bones. These two bones, identified as interparietal bones, were articulated by interdigitating sutures, to both of the adjacent bones as well as to each other. The presence of such bones is common in lower animals including lower mammals like rodents and marsupials but is rare in man. Os Incae have considerable clinical significance because they can be mistaken for fracture fragments during skull roentgenogram as well as during medico-legal autopsies. Besides, they can pose as a problem during neurosurgery. Sexual dimorphism, race and ethnicity cause significant variations in their incidence and hence, they are of considerable interest to anthropologists.