BY R BROOM. 483 



advocated by Wilson."^ In his paper published by this Society 

 he gives a very accurate and minute description of the bone and 

 its relations, and gives reasons for considering the bone to be a 

 true vomerine element and no part of the premaxillary. His 

 main arguments may be briefly summarised as follows : — (1) That 

 as the posterior part of the palatine plate of the dumbbell bone 

 rests on the " cartilage of the nasal floor " it is on a higher plane 

 than the maxillary palate ; (2) that the vertical part is prolonged 

 l)ackwards for a considerable distance dorsad of the maxillary 

 l^la.ne, and " that a bone which is so prolonged backwards on a 

 higher plane than the maxillary palate cannot be regarded as 

 developed in the same morphological plane with it "; and (3) that 

 the posterior spur is separated from the maxillary palate by 

 a peculiar hiatus. These arguments afford practically con- 

 clusive proof that the dumbbell-shaped bone belongs to the 

 vomerine category and is no part of the premaxillary; and to 

 Wilson thus belongs the credit of having first clearly recognised 

 the vomerine nature of the bone. But on the other hand, while 

 the above arguments show that the bone is not part of the pre- 

 maxillary, they rather support than disprove its homology with 

 the element usually called "palatine process of the premaxillary," 

 and Wilson himself recognises the weight of evidence in favour 

 of this homology; and when once it becomes recognised that the 

 palatine process of the premaxillary is itself a distinct vomerine 

 element anchylosed or formed in connection with the premaxillary 

 the difficulty of reconciling the two views at once disappears. 

 W. N. Parker,! in his recent paper on Echidna, gives a section 

 -of a young rnithorhynchus skull which shows the dumbbell- 

 shaped bone developing as bony splints to the cartilages of 

 Jacobson in exactly the same manner as Kitchen Parker has 



• J. T. Wilson, " Observations upon the Anatomy and Relations of the 

 dumbbell-shaped bone in Ornilhorhi/nchvs, with a new theory of its 

 homology, &c." Proc. Linn. Soc. N.S.W. 1894. 



t W. N. Parker, "On some points in the Structure of the Young of 

 JEchidna aculeata." Proc. Zool. Soc. 1894. 

 F F 



