William Clark was Professor of Anatomy at Cambridge for nearly fifty years, collecting many specimens of bones for use in the study of comparative anatomy, physiology and osteology. These formed a principal part of the collection that eventually became the university's Museum of Zoology. He wished to support students of natural sciences in acquiring knowledge from direct observation of well arranged and accurately identified specimens. The 1,289 items, catalogued in 1862, include 128 from humans of various races and dates. These include masks of the faces of Isaac Newton, William Pitt and Benjamin Franklin. This focus reflects, in part, the nineteenth-century fascination with phrenology. A regular participant in the influential Cambridge Philosophical Society, in May 1860 William Clark made there what Darwin perceived to be a 'savage onslaught' on his recently published On the Origin of Species. This book reveals Clark's very different approach to studying the tree of life.