154 PROF. G. B. HOWES ON jacobson'^s [Feb. 17, 



and Marsupialia as consisting, in the young animal, of a series of 

 distinct elements, for the most part paired, which he asserted ^ may 

 be (Cuscus) as many as ten in number. Sutton, following in the 

 same wake, has proposed to homologize the " prepalatine " centre of 

 the mammalian maxilla with the vomer of the Ichthyopsida, and to 

 interpret the vomer of the former as the paras]:)heuoid of the latter. 

 He relies chiefly upon dit-coveries of Albrecht's, which have been 

 shown by Sir W. Turner ^ to be of exclusively pathological interest ; 

 and, even were this not eo, the subsequent researches of Parker are, 

 in themselves, sufficient to show that his conclusions will not stand 

 the test of further inquiry (c/. infra). The joint observations of 

 these three observers, however, testify to a feeling af doubt as to the 

 exact homologies of those hones lying about the hase of the septiim. 

 nasi and its immediately adjacent structiires. 



The vomer of the Ichthyopsida and lower ilmniota, be it paired or 

 single, is invariably a non-repetitional bone lying immediately behiud 

 the premaxilla ; and there is considerable evidence to show that the- 

 apparently " single vomer " of some of these animals really represents 

 the pair so often present, in a confluent condition. When, in accom- 

 modation to the enlarging olfactory organ and tlie posterior nares, this 

 bone becomes shifted backwards or laterally expanded, its anterior 

 extremity generally remains true to its relationship with the pre- 

 maxilla. It is necessary to stand firmly upon these facts in dealing 

 with the question now in hand. 



Parker's observations show, among other things, that there is no- 

 constancy of position and extent of the apparently single portion of 

 the vomer of young mammals. They thereby completely undermine 

 the older conception of that bone, based upon analogy to the adult 

 man, which regarded it as a median element. They suggest, with 

 much forcibility, that we may the more reasonably look upon the 

 mammalian vomer in all its variations as morphologically paired^ 

 and that the argument deduced above from the study of tiie vomers 

 of ttie Ichthyopsida and lower Amniota may apply throughout. 

 With this Sutton's second conclusion above cited must remain 

 in abeyance. 



Chief among the supernumerary elements which Parker has de- 

 scribed as giving origin to the Mammalian vomers, together with the 

 palatine processes of the premaxillae, are certain bilaterally sym- 

 metrical ossicles to which he applies the terms " anterior " and 

 "posterior paired vomers." Critical examination of his mono- 

 graph will show that he has in all probability described the same 

 elements in some embryos as " posterior paired vomers," and in 

 others as " ethmo-turbinals ; " and further investigation must show 

 whether he has, as I believe, or has not confused the two with each 

 other, if with nothing else. Concerning his " anterior paired vomers," 

 however, there is less, if any, room for doubt. He has shown that 

 these, together with the " palatine processes " of the preraaxillse, may 

 arise early, before the full differentiation of the bodies of the pre- 



^ Loc. cit. pp. 270-271. 



= Jouru. Anat. & Phys. vol. lis. p. 198 (1885). 



