Ornithorhynchus anatinus, anterior rostrum of ‘mammary foetuses’ in ventral view, modified from Wilson (1901). A, model i (Wilson 1901: plate xxxvii, fig. 3); B, model ii (Wilson 1901: plate xxxviii, fig. 7). For broader anatomical context, see Figure 6. Wilson’s original abbreviations: al.n., alinasal cartilage; al.n.t., alinasal turbinal ridge; J.c., Jacobson’s (vomeronasal) cartilage; J.c’., posterior extremity of Jacobson’s cartilage; J.o., Jacobson’s (vomeronasal) organ; m.c., marginal cartilage; mx., maxilla; mx’., palatine plate of maxilla; n.d., nasal duct proceeding along outer surface of alinasal wall; n.d’., nasal duct passing inward and piercing alinasal near its ventral border; n.f., nasal floor cartilage; n.p.c., naso-palatine foramen (= incisive foramen); o.c., os carunculae; p.px., [medial] palatine process of premaxilla; pr.n., pre-rostral notch in marginal cartilage; p.vo., prevomer; px., body of premaxilla; px’., cut left premaxilla; px.l, cut left premaxilla; r.m.c., rostral marginal cartilage; s.n., septum nasi; s.n’, septum nasi where it descends and is intercalated into and continuous with nasal floor cartilage; sn”, edge of ventral border of septum nasi which is largely hidden by vomer; s.p.c., transverse cartilaginous lamina; vo., vomer.