AUTHOR « ABSTRACT OF THIS PAPER ISSUED 

 BY THE BIBLIOGRAPHIC SERVICE, AUGUST 4 



THE ONTOGENY AND PHYLOGENY OF THE STERNUM 



FRANK BLAIR HANSON 



Zoological Laboratory of Washington University, St. Louis, Missouri 



TWELVE PLATES (FORTY-NINE FIGUKES) 



CONTENTS 



I. Introduction 41 



II. Critical estimate of existing theories 42 



1. Ruge's theory of costal origin 42 



2. Paterson's coracoidal theory 43 



3. Work of Parker and Howes 45 



4. Whitehead and Waddell's 'in situ' theory 47 



5. Work of Rathke, Kravetz, Mueller, etc 52 



III. The ontogeny of the sternum 58 



1. The sternal bands 58 



2. The anterior median sternal rudiment 60 



3. The sternebrae 61 



4. Stages in the ontogeny of the mammalian sternum 63 



5. Conclusions 63 



IV. The phylogeny of the sternum 64 



1. Fishes 64 



2. Amphibia 66 



3. Reptiles 70 



4. Birds 76 



5. Monotremes 78 



6. Marsupials 78 



7. Aquatic mammals 81 



8. The adult human sternum 83 



9. Conclusions 87 



V. Summary 88 



I. INTRODUCTION 



The shoulder-girdle complex presents some of the most fasci- 

 nating and difficult problems of vertebrate morphology. In all 



the lower vertebrates the sternum, because of its intimate re- 

 lation to the coracoids, enters into and constitutes one of these 

 problems. Its origin, development, and homologies have been 



41 



