Between the last decades of the 18th century and the middle of the 19th century, something of paramount importance happened in the history of anthropology. This was the advent of a physical anthropology that was about the classification of ‘human races’ through comparative measurement. A central tool of the new trade was diagrams. Being inherently about relations in and between objects, diagrams became the means of defining human groups and their relations to each other – the last point being disputed (...) between the monogenists and the polygenists. James Cowles Prichard, a proponent of the comparative historical approach, was able to do without images in his pioneering Researches Into the Physical History of Man of 1813, but the third edition, which appeared in five volumes between 1836 and 1847, was richly illustrated with ‘ethnic types’ and skulls, including diagrams. What was happening is a process I engage with in detail for Samuel George Morton, who collected and distributed human skulls as lithographs in Crania americana (1839) and Crania aegyptiaca (1844). Along with the paper skulls travelled detailed instructions of how to look at them through a set of lines and to set their individual parts in relation to each other as well as to those of other types. Drawing on Johann Friedrich Blumenbach and Peter Camper, the Crania thus played a pivotal role in establishing what I call a diagrammatics of race – a diagrammatics that became overtly political with Types of Mankind (1854), which was written in Morton's honour by Josiah Nott and George Gliddon. (shrink)