Figure 2. Spatial layout of PAC relative to HG. Surface patches containing the two primary mirror-symmetric tonotopic maps (“high-low-low-high, hA1 and hR) were selected from the cortical surface meshes (n = 20 hemispheres) and are plotted here with the borders of HG indicated (solid lines: anterior border = FTS; posterior border = HS). In 9/20 hemispheres, HG was a single gyrus with a smooth crown. In 8/20 hemispheres (partial duplications *), an SI was present on the gyral crown (dotted lines) splitting HG into two divisions that remained connected by a common medial stem. In 3/20 hemispheres (complete duplications **), a dividing sulcus was present that reached all the way down to the medial base of HG so that the two divisions did not remain connected by a common medial stem (also indicated with dotted lines). Note that in the case of complete duplications, there is a difference in the standard nomenclature and there are considered to be two Heschl's sulci (HS1 and HS2): the dividing sulcus (dotted line) is HS1 and the posterior border (solid line) is HS2. In some cases, the posterior end of the functional maps extended onto less prominent gyri of the planum temporale, which are also indicated by dotted lines (outside the posterior border of HG) when present. These plots reveal a continuous anatomical–functional relationship across the anatomical variants of HG, as described in Results. As shown in the lower left inset, gyral/sulcal borders were drawn corresponding to cortical surface transitions between convexity and concavity, as described in Material and Methods.