52 FRANK BLAIR HANSON 



The paired rudiments, or sternal bands, also arise very early, 

 according to Whitehead and Waddell, 'in situ,' one on either 

 side of the body and unattached in the earlier stages to the 

 ventral extremities of the ribs. The paired rudiments ante- 

 date the appearance of the median rudiment. 



While Whitehead and Waddell and Paterson are very far from 

 being in accord as to the origin of the sternal rudiments, they 

 agree in demonstrating that the attachment of ribs and sternum 

 is a secondary fusion of parts, and that Ruge, while essentially 

 correct in his description of the stages he had under observation, 

 did not have the earlier stages and therefore was not in a position 

 to frame a theory of sternal origin. Without stopping now to 

 consider the relative merits of these two later theories, it must 

 be pointed out that their united efforts in overthrowing the Ruge 

 theory are of great value because of the hitherto widespread, 

 almost universal acceptance of this view. 



5. Work of Kravetz, Rathke, Mueller, etc. 



Kravetz ('05) worked on the pig. His youngest stage (24 mm.) 

 was also the oldest stage of Whitehead and Waddell. In the 

 24-mm. pig he found that the first ribs did not reach the sternal 

 rudiment, and, from the conditions in a series of later stages, 

 came to the conclusion that primarily there is no connection 

 whatever between the sternal rudiment and the costal cartilages 

 at their ventral ends. 



Bruch ('52) describes the early stage of the sternum as two 

 longitudinal rods, one on either side, which later unite with each 

 other and with the ribs of their respective sides. He thus in- 

 directly denies a costal origin, but fails to indicate just what his 

 views were in this respect. It is highly probable that the ques- 

 tion was never raised in his mind at that early date. Whitehead 

 and Waddell add but little to the description of this early worker, 

 except that they have a theory of 'in situ' origin for the struc- 

 ture in question. 



Rathke ('48) has an early, but very important paper in con- 

 nection with this discussion. His views are set forth in two short 

 paragraphs which are quoted in full as follows : 



