BY PROFESSOR J. T. WILSON, 733 



Plate xxxviii. 



Fig. 7. Ventral view of Model ii. 



pr.n., prerostral notch, between rostral prolongations of marginal cartilages, 

 r.m.c; px'., anterior trabeculee of premaxillae, fused here; p.px., palatine 

 processes of premaxilla; px.L, cut surface of continuity with ventral lamina 

 of left premaxilla; px., ventral lamina of right premaxilla; n.f., nasal floor; 

 s.n'., ventral edge of nasal septum where it enters into constitution of nasal 

 floor; J.C., cartilaginous floor of capsule of Jacobson's organ; ^. ro. , bilateral 

 prevomerine elements (anterior portions only) representing the dumb-bell 

 ossification. 



Fig. 8. Dorsal view of Model ii. 



al.n'., anterior border of alinasal cartilage, with nasal duct {n.d.) turning 

 inwards in front of it to enter the nasal cavity. Rest of lettering as in other 

 figures. 



Fig. 9. Sagittal section close to right of septum in anterior two-thirds, and 

 lateral view of posterior third of Model iii. (foetal Echidna). Here the os 

 carunculse is seen as a very small bony nodule {o.c.)\ the premaxillary 

 trabeculas {px'.) extend into, but not through, the shallow prerostral notch, 

 of which only the left boundary {r.m.c), formed by the rostral prolongation 

 of the left marginal cartilage, is seen. 



f.J.c. , opening in anterior part of capsule of Jacobson's organ; c.p., cartila- 

 ginous process prolonged backwards from alinasal wall behind and below 

 narial aperture. Other letters as in other figures. 



Fig. 10. Anterior view of Model iii., the right anterior part of the model 

 being cut away. 



al.n., cut edge of alinasal continued ventrally into cartilage behind anterior 

 narial aperture; cap. a., anterior cartilaginous margin of anterior narial 

 aperture; c.ap.p., the posterior cartilaginous margin of narial aperture. 

 Other letters as elsewhere. 



Plate xxxix. 



Fig. 11. Ventral view of Model iii. 



pr.n., shallow prerostral notch; pxL, short and abruptly truncated pre- 

 maxillary trabecula; jo .^x. , short palatine process of premaxilla; j^a:. , ventral 

 lamella of body of premaxilla; n.p.c, cartilaginous gap corresponding to 

 naso-palatine canal; p.p.c, short and isolated cartilaginous rod forming 

 skeletal basis of papilla palatina (c/. Broom, 11, "p.c"). This corresponds 

 with the palatine cartilage described by Broom in the papilla palatina of 

 various Marsupials, and figured by him in Perameles (7, fig. 6, "^^.c."); 

 s.p.c, is the transverse cartilaginous lamella which develops as the skeletal 

 basis of the secondary palate, and is to be compared with the corresponding 

 lamella in Ornithorhynchus as seen in fig. 3, s.p.c; al.n./., nasal floor formed 

 by the ventral extension of the alinasal cartilage; s.n'., triangular depressed 



