OCR Text |
Show 1885.] MISS B. LINDSAY ON THE AVIAN STERNUM. 6S5 occasional centres of ossification in the human sternum, and by median apophysis of the avian furcula. So far as regards the sternum of the higher Mammalia, the balance of recent evidence is certainly not in favour of the theory under consideration. The costal origin of the manubrium sterni is asserted by Ruge on the ground of embryological evidence ; while the complexity of its centres of ossification, so fully discussed by Prof. Albrecht in his recent paper on the human sternum, points to an origin from the fusion of many serial members, rather than from the differentiation of an interclavicle-a process, it may be added, which could have had no raison d'etre in a bone placed under conditions involving comparatively little mechanical strain. With regard to the avian sternum, on the contrary, no recent evidence has been offered in opposition to the theory maintained by Gotte and Hoffmann, which asserts the presence of an interclavicular element united with the costal sternum, and forming the crista sterni or keel1. This theory will be examined from a critical point of view in the following communication, the object of which is to discuss the origin of the avian sternum and its various parts. The communication consists of three sections, arranged in the following order:- PART I. (i.) Statement of the chief views held as to the nature of the Avian Sternum, and of the nomenclature of its parts adopted by the best authorities, where this offers any special peculiarity ; (ii.) Comments on certain of the above views. P A R T II. Details of the embryonic development of the sternum and adjacent parts in five types of bird (with Plates). P A R T III. Summary of the conclusions apparently suggested by the latter, in connection with previously recorded facts. 1 It should be added at the outset that no conclusion can be gained from the consideration of other types than birds; for while on the one hand we may refer to the keel of the sternum in Bats, which is admittedly the outgrowth of the sternum itself, belonging both to the presternum and mesosternum, yet on the other hand we must admit the existence in Hatteria of a keel formed by coalescence of the interclavicle with the sternum, and affording attachment to the pectoral muscles (see " Contributions to the Anatomy of Hatteria, or Bhyn-chocephalus of Owen," by A. Gunther, M.A., Ph.D.: Phil. Trans. 1867, p. 5CJ5). |