1885.] MISS B. LINDSAY ON THE AVIAN STERNUM. 6&5 



occasional centres of ossification in the human sternum, and by the 

 median apophysis of the avian furcula. 



So far as regards the sternum of the higher IMammaUa, the 

 balance of recent evidence is certainly not in favour of the theory 

 under consideration. The costal origin of the manubrium steini 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 strahi. 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 keel'. 

 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. 



Part II. Details of the embryonic development of the sternum 

 and adjacent parts in five types of bird (with Plates). 



Part 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 conoliision 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 mesosternuiu, 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 Ehyn- 

 chocephalus of Owen," by A. Giinther, M.A., Ph.D. : Phil. Trans. 1867, p. 595). 



