Clusters of neurons involved in color vision are identified by histochemical localization of cytochrome oxidase. The section was cut parallel to the pial surface and predominantly through layers II and III of the occipital lobe of the visual cortex in a rhesus monkey (inset). Cytochrome oxidase activity is greater in the dark regions than in the light regions. In area 17 (primary visual cortex), regions that have high cytochrome oxidase activity have a spherical shape in cross section and are cylindrical in three dimensions. Cytochrome oxidase staining in area 18 (secondary visual cortex) reveals thick and thin stripes rather than the polka-dot pattern. (Courtesy of Drs. Margaret Livingstone and David Hubel, Harvard University.) Source: The Visual System, Neuroanatomy Text and Atlas, 4e Citation: Martin JH. Neuroanatomy Text and Atlas, 4e; 2016 Available at: https://neurology.mhmedical.com/DownloadImage.aspx?image=/data/books/1854/marneuro14_ch7_f014.png&sec=129945521&BookID=1854&ChapterSecID=129945453&imagename= Accessed: October 15, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved