Ornithorhynchus anatinus, cranium, atlas, and partial axis in ventral view, modified from Meckel (1826: table IV, fig. I). Meckel’s original abbreviations: a, cartilago naso-labialis; b, os intermaxillare internum; c, os intermaxillare externum; e, os maxillare superius et palatinum; f, apophyses pterygoideae, mobiles; g, alveolus dexter; h, dens molaris sinister; i, choana; k, porus acusticus, in sinistro latere adstant annulus et os posticum, aut stylum aut malleum referens.

  Part of: Wible JR (2022) The history and homology of the os paradoxum or dumb-bell-shaped bone of the platypus Ornithorhynchus anatinus (Mammalia, Monotremata). Vertebrate Zoology 72: 143-158. https://doi.org/10.3897/vz.72.e80508