ABSTRACT:The basilar process of occipital bone is formed by fusion of the first three primitive vertebrae (or occipitoblasts), the most caudal of which is so-called occipital vertebra or pro-atlas. The failure of distal occipitoblasts to fuse with others gives rise to abnormal bone formations on the external surface of skull around foramen magnum, phenomenon called as "manifestation of occipital vertebra". Bone anomalies related to failure of segmentation of the most caudal occipital sclerotomes are rare, but have been identified. The anomaly leads to abnormal bone formation in the region of anterior rim of foramen magnum, either in the midline and or laterally. The anomaly has been occasionally referred to as third condyle, remanants of occipital vertebra, un-formed bone masses on the anterior rim of foramen magnum and prebasi-occipital arch in combination with an odontoid bone. The basiocciput of 100 Indian adult human skulls were examined for the presence of precondylar tubercles, which are single or paired osseous formations anterior to the occipital condyles and foramen magnum. Out of these 100 skulls, one skull displayed unilateral tubercle and the other bilateral tubercles.

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Optic canal is formed by two roots of lesserwing and body of sphenoid bone. It transmits optic nerve, ophthalmic artery and periarterial sympathetic plexus. During demonstration classes for undergraduate students we observed optic canal of left orbit of the adult skull, showing a thin spicule of bone which divided optic canal into two. Unilateral presence of duplicated optic canal is very rare. This case report may be useful for surgeons and radiologists.

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