Despite its clinical importance, the surface anatomy of the pterion is inconsistently reported. This study reappraises the surface marking of the pterion and its relationship to the middle meningeal artery (MMA). The position and morphology of the pterion were analyzed in the Frankfurt plane in 76 adult skulls and 50 adult cranial cone beam CT scans. Relationship to the anterior branch of the MMA was examined in the skulls. Measurement reproducibility was assessed in a 20% randomly selected sample. In the skulls, the majority of pteria were sphenoparietal (78%), followed by epipteric (16%) and frontotemporal (5%). The center of the pterion was a mean of 26 ± 4 mm behind and 11 ± 4 mm above the posterolateral margin of the frontozygomatic suture; measurements were reproducible and consistent between sides and genders. Distances from the frontozygomatic suture were slightly greater (29 and 16 mm, respectively) in cranial CTs. A one centimeter circle centered on the midpoint of the pterion overlapped the anterior branch of the MMA in 68% of skulls; the artery was a few millimeters posterior in the remainder. Mean skull thickness at the midpoint of the pterion was 4.4 mm compared to 1 mm at its thinnest point in the squamous temporal bone. In conclusion, in most adults, the pterion lies within a one centimeter diameter circle 2.6 cm behind and 1.3 cm above the posterolateral margin of the frontozygomatic suture (which is easily palpable in vivo). This region overlaps the anterior branch of the MMA in two-thirds of cases.

Fundamental mathematical relationships are widespread in biology yet there is little information on this topic with regard to human limb bone lengths and none related to human limb bone volumes. Forty-six sets of ipsilateral upper and lower limb long bones and third digit short bones were imaged by computed tomography. Maximum bone lengths were measured manually and individual bone volumes calculated from computed tomography images using a stereologic method. Length ratios of femur : tibia and humerus : ulna were remarkably similar (1.21 and 1.22, respectively) and varied little (<7%) between individuals. The volume ratio of femur : tibia was approximately half that of humerus : ulna (1.58 and 3.28, respectively; P < 0.0001). Lower limb bone volume ratios varied much more than upper limb ratios. The relationship between bone length and volume was found to be well described by power laws, with R 2 values ranging from 0.983 to 0.995.The most striking finding was a logarithmic periodicity in bone length moving from distal to proximal up the limb (upper limb k = 0.72, lower limb k = 0.93). These novel data suggest that human limb bone lengths and volumes follow fundamental and highly conserved mathematical relationships, which may contribute to our understanding of normal and disordered growth, stature estimation, and biomechanics.