^ONTOGENY AND PHYLOGENY OF THE STERNUM 83 



costocoracoid ligament to be the remains of an embryonic cora- 

 coid occurring in man or only the rudimentary indication of 

 man's phylogenesis. If this interpretation of the costocoracoid 

 ligament as the evidence of a coracoidal connection with the 

 sternum be correct, then from the elasmobranch to man the 

 closest relation between coracoids and sternum is maintained. 

 On the other hand, if Huntington's hypothesis is not sustained 

 by later investigation, no harm is done to our attempt to over- 

 throw Ruge's theory, for Rathke, Paterson, Whitehead and Wad- 

 dell, and myself have already shown that in man and other 

 mammals the sternum is an established structure prior to the 

 union of ribs with it. 



8. The adult human sternum 



In the literature of the adult sternum in man there is evi- 

 dence of a secondary, but interesting and corroborative sort. 

 It may be related back to the tendency of the ribs to grow toward 

 the ventral median line and fuse or articulate with each other, as 

 was noted in Chamaeleo. This has been shown by several 

 workers, Cunningham ('90), Dwight ('90), Tredgold ('97), Pat- 

 erson ('09), and Lickley ('04), to be especially prominent in the 

 human subject. Lickley, whose work is typical, studied a 

 series of fifty-one human sterna with special reference to the 

 relations of the seventh and eighth ribs to the sternum. 



The number of ribs reaching the sternum in Lickley's material 

 is shown in the following table : 



This constitutes a considerable percentage of variation at the 

 posterior end of the thorax, yet whether six or eight ribs enter 

 into union with the sternum, that structure is apparently not 



