Figure 19.2 (left): Hippocampus: Henry Gray, Anatomy of the human body,
20th rev. ed., edited by W. H. Lewis (1858; Philadelphia: Lea and Febiger,
1918), figure 739.
Chapter 21
Figure 21.1: Chimpanzee facial expression: C. Darwin, The expression of the
emotions in man and animals (London: John Murray, 1872), figure 18.
Figure 21.2: Muscles of the human face: C. Darwin, The expression of the emo-
tions in man and animals (London: John Murray, 1872), figures 1-3.