Interparietal and pre-interparietal bones in the population of south coastal Andhra Pradesh, India.

The squamous occipital bone consists of two parts: a cartilaginous supraoccipital part below and a membranous interparietal (IP) part above the highest nuchal line. The IP part develops from two pairs of ossification centres which form the two lateral plates and a median central piece. Any anomalous ossification of these centres gives rise to IP bones. Occasional separate ossified part of the IP region give rise pre-interparietal (PIP) bones which, when present, should be within the territory of the lambdoid suture. The present study was undertaken to observe the incidence of IP and PIP bones in skulls belonging to the south coastal population of Andhra Pradesh, India, hitherto unreported. In a total of 84 skulls, IP bones were found in 8 (9.5%) skulls and PIP bones in 6 (7.1%) skulls. The occurrence of IP and PIP bones can be correlated with the development of the squamous part of the occipital bones, and any alterations in the fusion of its ossification centres and its nuclei result in these anomalous bones. Knowledge of these bones may be important in dealing with situations resulting from fractures of occipital bones, and to rule out their incidence between races or populations in different parts of the world.