(Chapin & Lin, 1984, rat): the region considered as the SI cortex is not a cytoarchitecturally homogeneous structure but consists instead of a patchwork array of areas containing dense aggregations of layer IV granule cells, surrounded by granule-cell-sparse regions. As was shown by Welker (b71,b76), and in our own mapping studies (see Fig. 3), this discontinuous pattern of granular, or koniocortical, zones contains within itself a map of the ratbs cutaneous periphery. There are clear subtypes within this cytoarchitectural subregion, notably including the bgranular aggregateb type of cytoarchitecture characteristic of the paw, limb, and mystacial vibrissae areas, and the bbarrel-fieldb type (originally described by Woolsey and Van der Loos, b70) seen in the nose and perioral regions. In the mouse, but not the rat, such barrels also cover the whole whisker representation (Welker and Woolsey, b74). [ ]