Post natal development of the neck system in the chicken (Gallus domesticus)

The lengths of several neck muscles and tendons and the length, width, and height of the cervical vertebrae and some additional distances were measured in the chicken in six post-hatching ontogenetic stages and adults. Each vertebra is characterized by a unique combination of growth rates. All increase most in length. Cranial and caudal width as well as height decreases relative to length during ontogeny. When the long dorsal neck muscles are assumed to provide the support for the weight of the head and half of the weight of the neck, the neck system evidently develops according to McMahon's elastic similarity theory. The assumption is justified also because the weights of head and neck together appeared to scale as predicted by elastic similarity. Short neck muscles show negative and tendons positive allometric growth, and long neck muscles grow isometrically relative to neck length. This growth pattern of the muscles and tendons is a direct consequence of the geometric relations of the different growth rates of the vertebrae.