The dorsal third tier area in Galago senegalensis

Abstract

Five extrastriate visual field representations adjoin the anterior border of V-II in the owl monkey and collectively comprise a third tier of visual areas in this species. We have sought to determine whether the presence of a third tier of visual areas is a characteristic feature of visual cortex organization in primates. The order primates contains two suborders: the haplorhines (tarsiers, monkeys, apes and man) and the strepsirhines (lorisoids and lemuroids). We have found in a strepsirhine species, Galago senegalensis, that there exists a third tier of visual areas, one of which, the dorsal area, is described in detail in this paper. This finding together with recent evidence from haplorhine species suggests that a third tier of visual areas is a characteristic feature of visual cortex organization in primates.

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