Variability in dispersion among different stacks.

To assess variability in dispersion between stacks, we calculated for each stack the orientation standard deviation (SD) at normalized depths 0.2, 0.4, 0.6 and 0.8, as we already did for the entire distribution in Figure 3B. The 25th, 50th and 75th percentile of the SD values at each of these normalized depths are shown. Towards the proprial side (normalized depth 0.8), the SD showed a doubled variation among stacks (inter-quartile range (IQR) of 41°-25° = 16°) than at the adventitial side (normalized depth 0.2, IQR of 29°-21° = 8°). Overall, observations between samples consistently show a longitudinal orientation.