BY R. BROOM. 597 



Flower in supplying me with three mammary foetuses — one small 

 and two moderate-sized — of which I have sectioned the small one 

 and one of the large. 



Didelphys mttrina, L., (mammary ftetus, headUength 14 mm.). 

 In the young foetal Opossum the anterior portion of the nasal- 

 floor cartilage agrees veiy closely with the condition in the 

 Das3'ure; not onl}' is it comparatively flat, but from its ascending 

 inner plate it gives off a precurrent process to support the anterior 

 part of the septal ridge. In the plane of the papilla (fig. 1) the 

 premaxilla is seen giving off its palatine process. The nasal-floor 

 cartilage is here curved, the inner end passing up by the side of 

 the septal base into the septal ridge, while it is slightly depressed 

 into the hollow between the premaxilla and its palatine process. 

 A broad but not ver}^ thoroughly chondrified papillary cartilage 

 is seen in the section; and 1jy its edge the naso-palatine canal is 

 seen opening. In fig. 2 — a little distance behind — the nasal-floor 

 cartilage is found to have become divided as in Dasyurus, the 

 inner part having l:)ecome a well developed Jacobson's cartilage, 

 while the outer part has on this plane become lost. If this 

 figure be compared with fig. 2 of tlie Dasyure the close agreement 

 between the forms will be seen in the structure of Jacobson's 

 cartilage. There is, however, a slight difference in the relations 

 borne by the developing palatine processes to the cartilages. In 

 Dasyurus the palatine process is mostly infei'ior; while in this 

 form it lies within the lower half, the bottom ertd of the cartilage 

 being unsupported by bone. This though apparently a small 

 matter will be seen to be of considerable interest in connection 

 with the condition in the other forms to be described. In 

 Didelphys murina the septal ridge is more marked, the lower 

 corner of the nasal cavitj^ passing well in below it. The naso- 

 palatine canal will be noticed to have an almost vertical direction, 

 the obliquity being very slightly marked. The connections of 

 the canal with Jacobson's organ and with the nasal cavity are as 

 in Dasyurus, except that in Didelphys marina the organ Ijecomes 

 constricted into a little roundish duct-like canal before opening 

 into the nasopalatine canal. This little constricted j^art is not a 

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