54 FRANK BLAIR HANSON 



Charlotte Mueller ('06) worked out the development of the 

 thorax in a series of human embryos. She modeled the entire 

 thoracic framework, including vertebral column, ribs, and 

 sternum. The series of models as pictured in her paper are fine 

 examples of the possibilities in careful modeling of large and 

 complicated structures. However, her youngest stage had the 

 sternal bands, though remote from each other, firmly fused on 

 either side with the costal cartilages, and, following Ruge, she 

 describes the sternal bars as arising from the ribs. She makes 

 little other contribution to the subject of sternal genesis, for her 

 material, like Ruge's, was far too advanced for the early history 

 of this bone. 



1 1 is at once apparent that the theory of Parker, Ruge, Mueller, 

 etc., on the one hand, and those of Paterson, Whitehead and 

 Waddell on the other are mutually exclusive. But it would 

 seem that those of Paterson and Whitehead and Waddell have 

 only an apparent incompatibility, and that at least in so far as 

 their observations go, each was correct in reporting what he saw, 

 but the fact that they worked on very different forms and in- 

 terpreted their results in a widely different manner, leads to the 

 belief that they were- looking on opposite sides of the same shield, 

 and that it is possible to reconcile the two. 



The 'in situ' theory of Whitehead and Waddell is hardly to be 

 taken seriously. So ancient a structure as the sternum, dating 

 back to the Elasmobranchs, as we have seen, and found in every 

 higher group of vertebrates, including at least one or two teleosts, 

 and having an enormous and highly complex development in 

 many of the groups, can scarcely be accounted for in this simple 

 fashion. The 'in situ' theory took form from the material upon 

 which its authors worked. The pig is the basis of their main con- 

 clusions and this form is peculiarly unsuited for this work, 

 because of the degenerate character of the shoulder-girdle, which 

 is lacking at once in both clavicle and coracoid process (the so- 

 called subcoracoid now being thought to be an epiphysis). 

 For a proper interpretation of the sternum and shoulder-girdle 

 in the mammals those groups with well-developed clavicles, 

 episternals, suprasternal, and other appurtenances of this 



