Development of the chondrocranium in the domesticated fowl (Gallus gallus f. domestica), with a study on the variation of the of hypoglossal foramina

We critically review diverse literature on the cranial development in chicken, aiming at identifying potential areas of research in chondrocranial diversity that may relate to adult variation. Independent of the method used, there is general agreement regarding the onset of most chondrocranial elements. Inconsistencies in the literature concern the chondrification of specific elements as separate cartilage or continuous outgrowth of the preexisting cartilaginous element, the origin of fenestrations, the presence of certain cartilaginous structures (e.g., intertrabecular, cranial ribs), and the number of hypoglossal foramina. Intraspecific variation in the number of hypoglossal foramina in the red junglefowl and chicken is common, and known for other birds. The number of hypoglossal foramina lateral to the exoccipital bone varies between one and four in adult skulls of 75 individuals. To test for differences in chondrocranial shape between the fowl and chicken, timed stages of different breeds need to be investigated