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Show 154 PROF. G. B. HOAVES O N JACOBSON'S [Feb. 17, and Marsupialia as consisting, in the young animal, of a series distinct elements, for the most part paired, which he asserted 1 may be (Cuscus) as many as ten in number. Sutton, following in the same wake, has proposed to humologize the " prepalatine" centre of the mammalian maxilla with the vomer of the Lchthyopsida, and to interpret the vomer of the former as the parasphenoid of the latter. He relies chiefly upon discoveries of Albrecht's, which have been shown by Sir W . Turner2 to be of exclusively pathological interest; and, even were this not so, the subsequent researches of Parker are, in themselves, sufficient to show that his conclusions will not stand the test of further inquiry (cf. infra). The joint observations of these three observers, however, testify to a feeling of doubt as to the exact homologies of those bone^ lying about the base of the septum nasi and its iinmeuiatelv adjacent structures. The vomer of the Ichthyop-<idaand lower Amniota, be it paired or single, is invariably a non-iepetitional bone lying immediately behind 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 accommodation to the enlarging olfactory organ and the posterior nares, this bone becomes shifted backwards or laterally expanded, its anterior extremity generally remains true to its relationship with the premaxilla. It is necessary to stand firmly upon these facts in dealing with the question now iu 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 the vomers of the lchthyopsida 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 described as giving origin to the Mammalian vomers, together with the palatine processes of the premaxilla?, are certain bilaterally symmetrical ossicles to which he applies the terms " anterior" and "posterior paired vomers." Critical examination of his monograph will show that he has in all probability described the same elements in some embryos as " posterior paired vomers," and iu others as " ethmo-turbinals; " and further investigation must show whether he has, as I believe, or has not contused 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 premaxillse, may arise early, before the full differentiation of the bodies of the pre- 1 Loc. cit. pp. 270-271. 2 Journ. Anal. & Phys. vol. xix. p. 198 (1885). |