592 THE OKGAN OF JACOBSON IN MARSUPIALS, 



Ornithorliynchus," and some papers of my own where various 

 references are made to points in the Marsupial anatomy for 

 purposes of comparison. 



In the present paper I shall confine myself mainly to the 

 consideration of the general morphology of the organ and its duct, 

 Avith their cartilaginous and bony relationships, and their vascular 

 and glandular connections in typical members of the chief groups 

 of Marsupials, and to the morphological significance of the various 

 peculiarities met with. In discussing the various forms, I shall 

 adopt tentatively^ the classification as given in Thomas' " British 

 Museum Catalogue of Marsupials and Monotremes"; and as the 

 polyprotodont Marsupials have long been recognized as the more 

 generalised — a view which is confirmed by the study of the region 

 under consideration — it will be convenient to examine these first. 



DASYURID^. (Plate xli.) 



Of this group I have studied, (1) Early mammary ftttal 

 Phascologale peniciUata, (2) mammary foetal Dasyurus viverrinns, 

 (3) two-thirds grown D. viverrinus, and (4) adult D. maculafus. 



If a series of transverse sections be made of the anterior pavt of 

 the snout of Echidna, it will be found that there passes out from 

 each side of the base of the septum a flat cartilage, forming a floor 

 to each nasal cavity. In the very young animal, as shown l^y 

 Newton Parker, this cartilage is well developed, but in the adult 

 it only remains as a floor to the inner half of the nasal cavity. 

 On reaching the plane of the naso-palatine canal, this nasal floor 

 cartilage is found to divide into an inner and an outer part. The 

 inner becomes the cartilage of Jacobson's organ, while the outer, 

 much reduced just behind the region of the naso-palatine canal, 

 on passing backwards becomes more developed and passes inwards 

 below Jacobson's organ, uniting with the corresponding cartilage 

 of the other side Although there is no similar development of 

 the posterior outer part of the nasal floor cartilage in any Mar- 

 supial yet examined, the mode of division of the two parts and 

 the structure and relations of the anterior part of Jacobson's 

 cartilage will he found to have an almost perfect counterpart in 

 the corresponding structures of the Daysure and its allies. 



