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refers to a very deep fissure that separates the superior parietal lobule from the inferior parietal lobule of the primate. It is defined by dissection. In the human it separates the superior parietal lobule from part of the supramarginal gyrus of the inferior parietal lobule and from all of the angular gyrus of that lobule ( Duvernoy-1992 ). In the macaque it separates only the supramarginal gyrus of the inferior parietal lobule from the superior parietal lobule ( Martin-2000 ).
In both species the sulcus extends deep into the folds of cerebral cortex, splitting at some levels to form one or two small convolutions that are not visible from outside the brain. In the human, small unnamed convolutions arise variably from the superior parietal lobule, the angular gyrus, or the middle occipital gyrus to form gyri in the lateral wall or floor of the sulcus ( Duvernoy-1992; Mai-1997 ). This complex intracortical pattern can extend from the origin of the sulcus at the boundary of the superior parietal lobule with the postcentral gyrus almost to the occipital pole ( Duvernoy-1992 ).
In the macaque, the hidden portion of the sulcus has been called the \'simian fossa\'. It contains a single buried convolution, the annectant gyrus, which arises from the supramarginal gyrus laterally and, medially, is continuous with the wall of the superior parietal lobule. Proceeding caudally, the sulcus ends in junction with the lunate sulcus of the macaque at the rostrodorsal border of the occipital lobe. There a part of the annectant gyrus may split off to form the floor of the lunate sulcus of the macaque, while the main part, surrounded on three sides by intraparietal sulcus, dives beneath the fused cortex of the occipital gyrus dorsolaterally and cuneus dorsally and medially. Further caudally, the sulcus may open onto the longitudinal fissure, exposing a bit of the annectant gyrus through the cuneus on the medial surface of the occipital lobe. The annectant gyrus and an equal segment of occipital gyrus fuse their ends around a horizontal oval of intraparietal sulcus and detach from the overlying cortex to form a flattened tube that continues a few millimeters caudally in occipital white matter ( Martin-2000; Dubach-2008 ). In the rhesus macaque ( Macaca mulatta ), the portion of the annectant gyrus that joins the lunate sulcus of the macaque follows a similar course ( Paxinos-2009a; Dubach-2008 ).
Equivalent structures are not found in the rat or mouse ( NeuroNames ).
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