Gross Anatomy of the Parietal Operculum

A precise anatomical localization of SII within the inferior parietal lobule must consider the sulcal arrangement surrounding the parietal operculum. On average, the anterior and posterior borders of the parietal operculum are, respectively, the central sulcus and posterior ascending ramus of the Sylvian fissure.218 An imaginary lateral extension of the postcentral sulcus points to the middle of the parietal oper-culum, which is relatively co-extensive with the horizontal ramus of the Sylvian fissure (Figure 2.5). This horizontal segment, from inspection of 67 brains, is found in 99% and 70%, respectively, of left and right hemispheres.232 It is twice as long on the left. Men with a consistent right hand preference show bilateral greater length horizontal rami; however, an asymmetry always exists, which is longer on the left.232 An inferior portion of the supramarginal gyrus lies immediately posterior and superficial to the parietal operculum in most brains.218 This gross anatomical location of the parietal operculum coincides with the position of SII in summary illustrations by Penfield179"181 and occupies that portion of the parietal operculum included within area 40, by Brodmann17 or area PF, of subsequent analyses (e.g., Reference 59).

FIGURE 2.5 Sulcal pattern surrounding SII. A. Selective sulci of the lateral parietal cortex. Anatomical abbreviations: CS- central sulcus; LS- lateral sulcus; IPS- intraparietal sulcus; Par- posterior ascending ramus of the Sylvian fissure; Phr- posterior horizontal ramus of the Sylvian fissure; PoCS- postcentral sulcus; 39- 40 Brodmann's cytoarchitectonic areas. B. MR anatomical sagittal image illustrates the most common sulcal pattern surrounding the parietal operculum. Curved arrow marks CS- short left arrow points to PoCS- and right short arrow indicates Par. [A is modified from Figure 1 and B from Figure 2 in Reference 218.]

FIGURE 2.5 Sulcal pattern surrounding SII. A. Selective sulci of the lateral parietal cortex. Anatomical abbreviations: CS- central sulcus; LS- lateral sulcus; IPS- intraparietal sulcus; Par- posterior ascending ramus of the Sylvian fissure; Phr- posterior horizontal ramus of the Sylvian fissure; PoCS- postcentral sulcus; 39- 40 Brodmann's cytoarchitectonic areas. B. MR anatomical sagittal image illustrates the most common sulcal pattern surrounding the parietal operculum. Curved arrow marks CS- short left arrow points to PoCS- and right short arrow indicates Par. [A is modified from Figure 1 and B from Figure 2 in Reference 218.]

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