28 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.57. 



similar chain of bones in the promammalian reptiles or batrachians; 

 that the articular has likewise in many instances been gradually 

 crowded out and lost, its function having been usurped by the 

 condjdoid process of the dentar^^; that this same fate has in varying 

 degree befallen the other jaw elements of the reptilian skull, save 

 the dentary and splenial. In contradistinction to the transposition 

 theory of the quadrate and articular this latter view may be called 

 the absorption theory of these elements. 



A consideration of the fate of the reptilian quadrate in the mam- 

 malian skull necessarily involves a discussion of the fate of the other 

 elements of the reptilian jaw as well, since there can be little differ- 

 ence of opinion apparently that the mammalia have been derived 

 by descent from the reptilia or batrachia, and that through some 

 changes which are attempted to be explained by these various hypo- 

 theses the present state of affairs has been brought about in the 

 mammals. If the quadrate has been transposed from its original 

 position as a suspensorium of the lower jaw and transferred to the 

 mammalian auditor}^ chain, having its function completely altered, 

 and the articular has been transformed into the mammalian malleus, 

 as claimed by the advocates of this view, then a concomitant postu- 

 late which may be said to be absolutely vital to this hypothesis, is the 

 complete and total absence of any element or homologous part in the 

 mammalian jaw representing the reptilian articular. For if it can be 

 shown that any element corresponding to this bone in the Reptilia 

 is ever found in any mammal, then the whole theory falls and can 

 not be considered to be explanatory of the fate of the quadrate, since 

 it is utterly inconceivable how this latter bone could have ever 

 been independently intercalated in the middle of a chain of bones 

 connecting the eardrum with the fenestra ovalis, and which by 

 common consent, all are agreed, have always been concerned in per- 

 forming the highl}^ important function of audition. 



Another very vital matter involved in a discussion of this subject 

 relates to the origin and manner of ossification of the various bones 

 herein considered, for without a clear and definite understanding 

 of just what is meant by the terms employed, as well as a precise and 

 intimate knowledge of the histological processes by vrhich these 

 bones are developed, we shall never be able to make any satisfactory 

 progress toward a final solution of the problem before us. It is very 

 easy to speak of cartilage bones, membrane bones, splint bones, etc., 

 as if they were perfectly and obviousl}^ distinct entities and to base 

 important and far-reaching hypotheses upon a lax understanding 

 of the subject, but can we always be sure that such conclusions 

 are sound? That there are broad and well-marked distinctions 

 between the various categories of ossifications, in their typical devel- 

 opment, is undoubtedly true, but at the same time the fact must not 



