560 MAMMALIAN PRENASAL CARTILAGE, 



here an opportunity of seeing the uncompKcated higher mamma- 

 Han condition, and though the bat is high in the scale of organ- 

 isation it will thus be well to consider it first. If a transverse 

 vertical section be made in the plane which passes through the 

 opening of Jacobson's organ into Stenson's duct there is seen (fig. 

 4) a delicate nasal septum (n.s.) which does not reach the level of 

 the nasal floor, with on either side of its base the usual cartilages 

 of the nasal floor (n.f.c), here distinct from the alinasals. 

 Inferiorly Stenson's ducts (n.p.c.) are seen passing up from the 

 palate with between them the papilla. Round the upper part of 

 the duct is a sickle-shaped piece of cartilage whose inner part, 

 surrounding what is practically the anterior part of Jacobson's 

 organ, is the anterior continuation of Jacobson's cartilage, and the 

 outer part of which is the similar continuation of Stenson's 

 cartilage. Between the portions representing Jacobson's cartilage 

 is found a small median mass {j).n.) which from its relations may 

 almost certainly be regarded as the prenasal. Posteriorly this 

 cartilage has no connection with the nasal septum, but it occupies 

 a position somewhat similar to that of the prenasal in the fcjetal 

 calf (fig. 7). A very little in front of this plane the small pre- 

 nasal is seen sending downwards two lateral plates which pass 

 one to each side of the papilla and thus forming its framework 

 {p.ii. fig. 5). There is no further anterior extension. Though 

 the downward lateral processes can hardly be homologous with 

 the lateral extensions of the prenasal in miiliorhynchus, they 

 illustrate potentialities of the structure usually latent. The con- 

 dition is, however, specially interesting as throwing light on the 

 peculiar structures found in the Marsupials. 



In both Diprotodont and Polyprotodont Marsupials there is in 

 the anterior part of the palate an unusually well marked papilla 

 which generally separates the naso-palatine ducts considerably. 

 It is remarkably developed in the Wombat and very well in the 

 Phalangers. In all the forms I have examined ( Macropiis, Tri- 

 cliosnrus, Dasijurus and Peramele^) this papilla is supported by a 

 cartilaginous jDlate. In the adult Trichosunts there is a median 

 ridge from which lateral plates pass off. Here and there the 



