Ornithorhynchus anatinus, 122 snout-tail length posthatchling, modified from De Beer and Fell (1936: table VI, figs. 22, 24). A, chondrocranium and B, posterior two-thirds of chondrocranium with bones in situ in ventral view (palatine removed from left side). De Beer and Fell’s original abbreviations: ali, Alisphenoid bone; at, Ala temporalis; bo, Basioccipital bone; bs, Basisphenoid bone; cm, Marginal cartilage of snout (crista marginalis); Epg, “Echidna-pterygoid’; et, Ethmoturbinal; fc, Carotid foramen; ff, Foramen for facial nerve; fio, Infraorbital foramen; fj, Foramen jugulare; fol, Foramen olfactorium advehens; fp, Foramen perilymphaticum; fpa, Palatine foramen; i, Incus; jug, Jugal bone; lta, Lamina transversalis anterior; m, Malleus; Mc, Meckel’s cartilage; mpf, Maxillopalatine foramen; mt, Maxilloturbinal; mxa, Alveolar process of maxilla; mxp, Palatine process of maxilla; mxz, Zygomatic process of maxilla; ns, Nasal septum; oc, Occipital condyle; pab, Palatine bone; pan, Pila antotica; pcs, Palatine commissure (of ectochoanal cartilage); pmp, Processus maxillaris posterior; pmx, Premaxillary bone; pns, Paries nasi; pra, Prearticular bone; ps, Paraseptal cartilage; ptg, Pterygoid (“mammalian”) bone; pv, Prevomer bone; pvp, Prevomerine process of premaxilla; sh, Stylohyal cartilage; sm, septomaxilla; spm, Egg-tooth fused to symphysis of premaxillae; sq, Squamosal bone; sqz, Zygomatic process of squamosal; tsy, Tectum synoticum; ty, Tympanic bone; Vn, Vidian nerve (palatine); vo, Vomer bone.