ONTOGENY AND PHYLOGENY OF THE STERNUM 47 



4. Whitehead and Waddell's 'in situ' theory 



In 1911 Whitehead and Waddell undertook to settle the whole 

 vexed question by a reexamination of all the evidence and by a 

 study of younger stages than had hitherto been used. Their 

 work was based on observations made upon three forms : the pig, 

 cat, and man. These studies, however, instead of settling the 

 dispute between the theories of Ruge and Paterson, led the 

 authors to reject both of them and to propound an entirely new 

 one. So, as a result of this latest paper, there are at the present 

 time three, instead of two, rival theories of sternal origin. For 

 neither of these two latter theories had been able of its own 

 weight effectually to settle the points in question ; Ruge's theory 

 of costal origin still maintains its hold upon the minds of most 

 morphologists ; but nevertheless, new evidence produced by later 

 work throws very strong doubt upon the conclusions of Ruge. 



Ruge apparently had no stage prior to that in which the sternal 

 bands were united with the costal cartilages; but it must be ad- 

 mitted, that his conclusions, based upon the material that passed 

 through his hands, are clearly valid for the stages described — 

 in fact, the only ones that could possibly be deduced therefrom. 

 It is probably this fact that gave Ruge's theory its persistence 

 through the years. The later workers, however, have had as 

 their goal stages much earlier than Ruge's, and, while they have 

 succeeded in finding them, are still very far apart in the inter- 

 pretation thereof. 



As Whitehead and Waddell's paper is of considerable im- 

 portance and has never been reviewed, a brief summary of its 

 contents and conclusions is necessary here. 



They studied first the pig, because the absence of clavicles in 

 this form tends to simplify matters at the cranial end of the 

 sternal rudiment; next the cat, for here the clavicle is a rudi- 

 mentary bone and does not articulate with the sternum, and 

 finally the human embryo, where the clavicle reaches its fullest 

 development. 



These authors began with pigs of 24 mm. and worked through 

 successively smaller stages, until the sternal rudiment was very 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 26, NO. 1 



