Abnormalities of the muscular anatomy in the shoulder region of paralysed chick embryos

Abstract

Chick embryos were paralysed with decamethonium during the time when the wing muscles were being formed by cleavage of the dorsal and ventral premuscle masses of the wing buds. Dosing with the drug was commenced at 5 days of incubation and was continued for periods ranging from 3 days to 1 week. Among the anatomical muscular abnormalities found in the paralysed embryos were various delays or failures of cleavage, a divergence of the proximal moiety of pars scapularis of the triceps away from the humerus, and a tendency for M. coracobrachialis posterior to be split into two portions. Although there were individual differences in details of the anomalies, a generally consistent syndrome of muscular aberrations prevailed throughout the experimental embryos. The results indicate that functional activity is important for the formation of a normal muscular anatomy. The abnormalities associated with paralysis suggest that tensile stresses arising from skeletal growth act in conjunction with those due to neurogenic contractions to influence the orientation of muscle fibres and their grouping to form individual muscles.