BY H. GROOM. 617 



in the carnivorous ^Marsupials and but feebly indicated in Pera- 

 meles, and there is also a veiy marked descending process by the 

 .side of the nasopalatine canal in the notch. The ascending and 

 descending processes are well seen in their adult condition in 

 PI. XLiv. fig. 4, representing the condition in the adult Pseudo- 

 chii'us, while their mode of development is well seen in Plate xlv. 

 representing the different stages of the young Trichosurus. By com- 

 paring PL XLiv. fig Jr. with, say PI. XLiii. fig. 1, — the condition in 

 the young Perameles, and fixing the two unquestionably homo- 

 logous parts — the processes passing into the inferior septal ridges 

 — the two additional processes will be readily seen. In the 

 primitive condition of the palatine processes there is also a marked 

 difference from that of any of the Polyprotodonts. In those 

 latter it is always apparently developed as a small curved splint, 

 supporting a considerable ax-ea of the cartilage. In the Phalan- 

 gers it is developed as a rod along the middle of the inner side of 

 Jacobson's cartilage. This would lead one to assume that the 

 middle region of Jacobson's cartilage in the Phalanger is probably 

 homologous with the lower third of the cartilage in Dasyurus, 

 which is the region where the palatine process first developed. 

 If this be so the downward pi'ocess in the Phalangers would 

 become the more manifestly an additional development. 



In its posterior parts Jacobson's cartilage follows much the 

 same lines as in the Polyprotodonts. The outer part of the ridge 

 process very early^ becomes separated into the outer bar of 

 Jacobson's cartilage, which, after being isolated for a short dis- 

 tance, becomes attached to the under part of Jacobson's cartilage, 

 and the condition differs little from that of the Polyprotodonts. 

 The organ itself is very similar to that in Dasyurus or Didelphys; 

 there is, however, one yeiy constant difference in that while in 

 the Polyprotodonts there is only a single blood vessel running 

 along the hilus, in the Phalangers there is a distinct plexus. At 

 the extreme anterior end there is usually one or two large veins, 

 and these on passing backwards divide into four or five large sub- 

 equal branches which run parallel along the hilus. This is a 

 character met with in the ^lonotremes, but it is probably not of 



