594 THE ORGAN OF .TACOBSON IN MARSUPIALS, 



Echidna as figured by jS". Parker, or in the adult as figured l)y 

 myself, the striking agreement will be manifest. 



In fig. 12 is seen the condition of the organ and its relations 

 in the region of its greatest development. The organ is almost 

 uval in section, there being but a very slight indentation of the 

 outer wall : the inner and lower walls of the oi'gan are about 4-6 

 times the thickness of the outer. Jacobson's cartilage is a curved 

 plate which supports the organ on its inner and lower sides. Tlie 

 palatine process of the premaxilla, here just commencing to ossify, 

 occupies the lower and inner side of Jacobson's cartilage. 



Near its posterior part the organ is reduced to a duct with 

 simple columnar epithelium, and the cartilage is present as a 

 narrow thick plate passing more outwards than downwards, and 

 forming a floor to the duct and its neighbouring developing glands. 



Dasyurus viverrinus, Shaw, (mammary fujtus, head length 

 15 mm.). In the somewhat older foetus of the common Dasyure 

 we have the same type, but with the later stage of development 

 the details are better seen. The nasal-floor cartilage is very 

 similar to that seen in the foetal Phascologale, but an additional 

 feature is revealed. From the point where the ascending inner 

 plate of the nasal-floor cartilage sends out the plate to support the 

 basal ridge a detached process of cartilage passes forward sup- 

 porting the feeble anterior part of the ridge. This is better seen 

 in the adult, and is interesting from the fact that a similar pre- 

 current process has not been found in any other form, except 

 Didelphys. 



Figs. 1 and 2 illustrate sections in the anterior jiart of tlie 

 nasal-floor cartilage. In fig. 2 the outer part of Jacobson's 

 cartilage is seen detached from the inner on one side. This little 

 detached bar is seen in fig. 4 to become connected with the lower 

 part of Jacobson's cartilage, and from its being almost invarial)ly 

 present throughout the Marsupialia connecting the upper with 

 the lower parts on the outer side, it will be referred to in the 

 following descriptions as the " outer bar of Jacobson's cartilage." 



In fig. 3 the naso-palatine canal is seen, on the right side opening 

 into the anterior end of Jacobson's organ. The organ has a veiy 



