Unusual features associated with cranial openings of optic canal in dry adult human skulls.

One hundred and eighty six dry adult human skulls (372 sides) were studied in order to reveal the presence of unusual features--such as recess, fissure and notch--in the cranial opening of the optic canal. Recess, an extension of the lateral wall, was found in 229 (61.5%) sides. Fissure, an irregular discontinuity above the lateral recess, was observed in 158 (42.4%) sides. Notch, a gap in the posterior-most limit of the roof, was seen in 66 (17.7%) sides. These were commonly seen bilaterally. The etiology of these was attributed to the development of the optic canal. During intrauterine life the optic canal is in the form of a large keyhole shaped foramen, which slowly transforms into the adult canal. A developmental arrest at an early stage may lead to the formation of recesses and fissures.