Note 173 — Chapter XXIII · GENERAL ACCOUNT OF THE SKELETON IN MAMMALIA (continued).
Reading edition
See E. Cope, "The origin of the foot structures of Ungulata," Journ. of Philad. Acad. 1874. H.F. Osborn, "The evolution of the Ungulate foot," T. Amer. Phil. Soc. 1889.