Motoneuron formation in the brachial spinal cord of the dystrophic chick embryo.

Motor neuroblasts comprising the brachial segments of the lateral motor column in the dystrophic chicken were counted at 6, 7, 9, 12, and 18 days of incubation and at 5 days' post-hatching. Comparisons with similar counts from normal chick embryos disclosed that there was a significantly greater depletion of motor neurons in normal embryos between days 9 and 12. These findings suggest that nerve-muscle interaction may be altered early in the development of the motor unit in the dystrophic chick embryo.