The Development of the Chicken Skull and the Histology of Some of its Sutures

Abstract

The use of differing definitions of homology has led to controversies about the identity of bony elements in vertebrate skulls. An example is the controversy concerning the identity of the avian frontal, which has been assigned that name based on its location and shape. However, developmentally, it has been suggested to be a fusion of the frontal and parietal (i.e. frontoparietal). To assist in resolving this controversy, a search for a suture in the gap between the two ossification centres of the chicken's frontal was attempted. The production of a staging table of the chicken skull revealed a putative suture would be found between stages HH36 and 37. Histological examination of the developing frontal failed to find any evidence of a frontal-parietal suture, leading to the conclusion that the avian frontal is a single element formed from two ossification centers and is not a frontoparietal. iii Acknowledgements I would like to acknowledge and thank several people who have helped make this thesis possible and encouraged me throughout the two very difficult years of my masters. Chief among these people is Hannah Feldmann whose encouragement, patience, dedication and belief in me has made it possible to finish this thesis despite the extreme difficulty in completing it. I would also like to thank her for helping me in a crucially important stage of the experiment where I needed a companion to stay with me overnight in the lab. I would also like to thank my family for emotional and financial support throughout the two years and for making it possible for me to reach the masters level. My family's never-ending support made my thesis achievable. My best friend Olivier Heldwein deserves a lot of gratitude for help in so many ways and on so many occasions, including experimental steps and use of his camera. Olivier provided emotional and scientific support to me during the execution and writing the thesis, for which I am grateful.