Distance between the first and second oblique vein of P. minor (Note: The data in the graph were measured from 42 samples. All the data can be roughly divided into three groups: distance less than 0.6 mm, distance greater than 1.2 mm, and distance between 0.7 mm and 1 mm, among which, individuals with distance less than 0.6 mm are the majority. The figure of the veins on the right, from top to bottom, represents the maximum, median and minimum distances, respectively. Units: mm).