BY R. BROOM. 611 



the nasal-floor cartilage is hollowed out to accommodate an anterior 

 projection of Jacobson's organ, but we are thereby enabled to 

 understand the different parts. If this section be compared with 

 PI XLV. fig. 3, the Trichosure condition, there is no trouble in 

 making out the homology of the diiferent parts. The inner plate 

 corresponds to that in Trichosurus, except that it does not curve 

 downwards at its lower end, but retains its connection with the 

 outer part of the nasal-floor cartilage. On the outer side of the 

 opening in the cartilage above the organ is seen a distinct knob 

 attached to the outer nasal-floor cartilage; this is unquestionably 

 the outer bar of Jacobson's cartilage, agreeing closely with the 

 condition in Trichosurus; while the upper opening in the cartilage 

 is due to the customary detachment of the outer bar from the 

 inner plate of Jacobson's cartilage. In PI. xlvi.. fig. 4 we have the 

 more usual condition revealed; almost the only difference, in fact, 

 from the similar section in Trichosurus (PL xlv. fig. 4) is due to 

 the absence or reduction of the inferior septal ridge in Maci'opus. 

 The naso-palatine canal opens into the organ and the nasal cavity 

 in the usual way. 



At its hinder end, as seen in PL XLVii. ng. 9, the organ is 

 situated well up the side of the septum, a condition recalling the 

 appearance in the human foetus. 



The organ itself is on the whole rather feebly developed, and 

 has the appearance of a degenerate Phalanger t}^e. There are 

 few glands anteriorly, and in the hilus are only a few small blood 

 vessels. 



Sub family P o T o R I N .E. (Plate xlvii. figs. 10-12.) 



^pyjiiymnus rufescens, Gray, (mammary fcetus, head length 

 15'5 mm.). In the Eat-Kangaroo, though we have a fairly close 

 agreement with the condition in Macropus, we have some remark- 

 able differences. PL xlvii. fig. 10 represents a section in the 

 plane of the 2nd upper incisors. The nasal- floor cartilage is well 

 developed, and at its inner part is found turning round to support 

 the inferior septal ridge more after the manner of the Polypro- 

 todonts than of the Phalangers. In the plane through the point 



