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Show 684 MISS B. LINDSAY ON THE AVIAN STERNUM. [June 16, 1840. 0. montana, Blyth, Proc. Zool. Soc. 1840, p. 77. 1840. 0. californiana, Blyth, ibid. 1851. O. montana, Audubon and Bachman (fig.). 1854. O. montana, Richardson, Voyage of H.M.h. Herald (osteological fig.). „ 1857. O. montana, Baird, Mammals N. America, Survey fteports, p. 673 (fig. of horn). 1859. O. montana, Schott, U. S. Mexican Boundary Report, part ii. p. 52. 1871. 0. canadensis, Blyth ( " Zoophilus " ) , The Field, May 13 (fig.). 1880. O. cervina, Alston, Biologia Centr.-Am., Mammal, p. 111. 1884. O. montana dalli, Nelson, Proceedings of U. S. National Museum, vol. vii. p. 13. 9. O n the Avian Sternum. By BEATRICE LINDSAY, Girton College, Cambridge \ [Received June 16, 1885.] (Plates XLII.-XLV.) Lntroduction. The most typical and simple form of the sternum is that found in Reptiles, where this bone, although associated with a shoulder-girdle of maximum complexity, and strengthened by the apposition of an interclavicle in the median line, is itself undoubtedly of homogeneous origin, that is to say derived solely from the fusion of ribs. In Birds and Mammals the sternum has been supposed by some authorities to be, on the contrary, a composite structure, containing a supplementary median element more or less distantly derived from membrane-bone, and homologous with the free T-shaped interclavicle of Reptiles. Much has been done to increase the plausibility of that theory by a vague use of the terms " interclavicle " and " episternum." These names, when first introduced, expressed nothing but a certain anatomical position of the parts to which they were applied ; but now that the aforenamed reptilian structure is held by nearly all anatomists to be a membrane-bone, the names given to it inevitably tend to suggest a meaning restricted to particular homologies. But, unfortunately, many authors still apply the said names indiscriminately to any anterior median ossification, or paired ossification approaching the median line, without regard to its origin, whether known or unknown ; and thus they unintentionally create factitious evidence for the above-named theory, by the continual implication of homologies which have never been satisfactorily proved. Instances in point are afforded by certain 1 Communicated by Dr. H. Gadow, C.M.Z.S. |