The origin and developmental mechanics of the avian sternum

Comparatively little work has been done on the development of the avian sternum. As previous publications on this subject are primarily concerned with phylogenetic problems, it occurred to the present writer to study the embryology of the avian sternum from the standpoint of developmental mechanics. This bone shows such remarkable adaptations to functional requirements in different species that the factors concerned in its development were likely to be of particular interest. Moreover, from the technical point of view, the embryonic bird’s sternum seemed very promising material. In the first place it would be very suitable for tissue-culture experiments, as its thin, flat shape would facilitate nutrition through the external surface; in the second place it has a very definite and characteristic form, so that abnormalities produced experimentally could be readily detected; and in the third place it does not ossify during embryonic life, so that structural complications resulting from bone deposition would be eliminated. It was decided first to study in detail the normal anatomical and histological development of the sternum and thus obtain as much information as possible about its normal morphogenesis. Points which could not be conclusively established by morphological evidence alone, or problems which could not be approached at all by ordinary morphological methods, would then be investigated experimentally by the tissue-culture technique.