The first part of the carotid canal runs upward and forward. This segment, which we call the ascending petrous part of the carotid canal (Lang and Schreiber 1983), forms an average angle of 122° with the FHP in neonates and 99.7° (86–114°) in adults. The canal then turns forward and medially at almost a right angle. This bend has been termed the petrous curvature. We found the distance from the external orifice of the carotid canal (lateral wall) to the supramastoid crest to be 17.3 (16–19) mm in neonates, 21.5 (18–23) mm at 3 years of age, 24.67 (24–25) mm at 8 years of age, and 28.4 (23–35) mm in adults (Lang et al. 1983).