BY R. BROOM. 607 



The ridge pi'ocess, on the other hand, so large in the Ringtail and 

 Flying Phalangers is only slightly develo2:)ed in Trichosurus. The 

 descending process is very distinct; and the palatine process more 

 developed vertically than in the younger fcetuses. In PI. XLV. fig. 

 S the naso-palatine canal passes up almost vertically and opens 

 into Jacobson's organ. At this stage there is no chondrification 

 of the outer bar. In the following figure the organ is closed; and 

 the naso-palatine canal is merged in the nasal cavity. Even in 

 this plane the outer part of the nasal-floor cartilage is still well 

 developed. Jacobson's cartilage is an almost vertical plate, and 

 the organ lies against it much flattened from side to side. 



Trichosurus vulpecula, Kerr, (adult). In the adult common 

 Phalanger there is considerable agreement with the condition in 

 the adult Petaurus. All the main peculiarities are due to two 

 facts — (1) a much less degree of development of the inferior 

 septal ridge in Trichosurus; and (2) a greater development of the 

 outer nasal-floor cartilage. 



In PI. XLVi. fig. 1 through the posterior papillary region, the inner 

 part of the nasal-floor cartilage is very similar to that in Petaurus, 

 except that the ridge process is more feeble here; the outer part 

 of the nasal-floor cartilage though small is, however, better 

 developed than in Petaurus. The papillary cartilage is well seen 

 in this plane and is interesting from its having a distinct median 

 ridge. In PL xlvi. figs. 2, 3 and 4, is seen the mode of division of 

 the nasal-floor cartilage, which is more complicated than in any 

 of the other common Marsupials. In the most anterior part of 

 the gap between the premaxilla and its palatine process there is 

 a most distinct, rather large, descending process filling up the 

 whole gap. On the naso-palatine canal passing up, and on the 

 premaxillary being farther removed from the palatine process, the 

 descending cartilaginous process remains only as a narrow internal 

 plate lying close against the palatine process (PI. xlvi. fig. 2). In 

 this plane the ridge process though small is distinct, and is con- 

 nected with both the inner plate of Jacobson's cartilage and the 

 outer part of the nasal-floor cartilage. In PI. xlvi. fig. 3, a very 

 little behind the pre\'ious plane, an anterior prolongation of 



