Comparative anatomy of chicken and human forelimb muscles: Implications for human congenital conditions through developmental models.

The chicken embryo is a well-established model for studying the fundamental principles of limb development and has been instrumental in investigating human limb conditions such as polydactyly and the effects of thalidomide. Chicken embryos are accessible, low cost, and can be manipulated both in ovo and in culture. Recent innovations in the genetic modification of chickens, including making transgenic reporter and targeted deletions, have transformed the potential use of the chicken embryo in developmental biology research. Specifically, there is now the potential to model human congenital limb conditions in chicken limbs to better facilitate surgical management of soft-tissue manipulation, particularly muscles, to correct force imbalances and restore functionality. Looking towards this new era of discovery research, we have used data from available literature combined with our own data and observations to determine homologies of human and chicken muscles. Although muscle homology is relatively well conserved across amniotes, there has been no direct comparison of chicken limb muscles with human limb muscles, preventing a direct translation of soft-tissue changes in chicken models of limb conditions to humans. From this study, we conclude that stylopod and zeugopod muscles are well conserved and are mostly homologous between chickens and humans. We also highlight species variations which are not yet described in literature. Finally, we offer examples of how our comparative data can be used to comment on previously elusive muscular changes in certain congenital conditions, such as radial dysplasia, for which surgical management remains challenging.