545 



ON THE MAMMALIAN AND REPTILIAN VOMERINE 



BONES. 



By R. Broom, M.D., B.Sc, C.M.Z.8., Corresponding Member. 



(Plates xxiv.-xxvi.) 



Eor a hundred years and more almost every anatomist of note 

 has agreed in regarding the paired elements which lie immediately 

 behind the premaxillaries in the reptilian palate as together 

 homologous with the mammalian vomer ; and the opinion of 

 authorities has been so unanimous that it is naturally with some 

 hesitation that one ventures to suggest that the currently accepted 

 view is probably incorrect. It is quite likely that this view might 

 have long continued to be almost universally accepted had not 

 the difficulty of explaining the homology of the dumbbell-shaped 

 bone of Urnithorhynchus forced us to a reconsideration of the 

 position. This little bone, whose anatomical relations and 

 development are now so well known, lies beneath the nasal septum 

 and clasps the cartilages of Jacobson. At no stage in its 

 development is it connected with either the vomer behind or the 

 premaxillaries in front. The earlier anatomists, Rudolphi, 

 Meckel, and Owen, very naturall}^ agreed in finding the homologue 

 of this little bone, which lies in front of the vomer, in the palatine 

 processes of the premaxillae of the higher forms; and in more 

 recent times this view has been supported by Albrecht, Turner, 

 Symington, and myself. But if this view be correct, it becomes 

 necessary to regard the premaxillary as a complex bone, and as 

 possibly representing more than the premaxillary of the reptilian 

 or amphibian ancestors. Before looking more closely into the 

 problem it may be well to briefly review one or two recent papers 

 dealing with the subject. 



