61 G THE ORGAN OF JACOBSON IN MARSUPIALS, 



neither attached to upper or lower borders. In Echidna, at the 

 posterior part of the organ, the upper connection gives way and we 

 have the irregular U-shaped appearance as in Marsupials. We may 

 tlius conclude that we have in the simple Marsupials a somewhat 

 degenerate Monotreme type, the outer bar being the rudimentary 

 remains of a primitive turbinal. 



In Didelphys and Perameles we have a short almost vertical 

 nasopalatine canal ; while in Dasyurus it is rather long and 

 oblique. In Perameles there is a small yet distinct downward 

 process of Jacobson's cartilage in the notch between the pre- 

 maxillary and its palatine process, a process which is more or less 

 developed in all the Diprotodonts, and apparently the forerunner 

 of the long anterior pi'ocess which supports Jacobson's duct in 

 the higher mammals of the Cat or Sheep type. In Didelphys 

 there is only a slight indication of this process; and in Das3airus 

 it is absent. From this we may consider that Dasyurus is the 

 more primitive. As regards the portion of Jacobson's cartilage 

 supported b}^ the palatine process all three genera differ. In 

 Dasyurus the support is on the lower edge and lower inner third; 

 ill Didelphys on the lower inner half ; while in Perameles the 

 whole inner side of the cartilage is supported by the palatine 

 process. In neither of the latter two genera, however, is the 

 lower edge of the cartilage completely supported by bone as in 

 Dasyurus. In all three genera there is but a single hilar vessel; 

 and as a rule the supply of mucous gland is scanty. Perameles 

 is peculiar in having a small anterior prolongation of the organ 

 in advance of the opening, as well as in the exti'eme shallowness 

 of the secondary palate. 



In the Phalangers we enter on a well differentiated type. The 

 most i-emarkable points of difference from the previous forms are 

 to be found in the complex nature of Jacobson's cartilage in the 

 anterior region There is a well developed inferior septal ridge 

 into which is sent a cartilaginous process from the ascending inner 

 part of tlie nasal-floor cartilage, and which is untjuestionably 

 homologous with the similar process in the Polyprotodonts. In 

 addition, however, there is an ascending process, only I'udimentary 



