The musculus complexus of normal and dystrophic chicken embryos.

Abnormalities have previously been reported in the pectoral muscle of embryos and young chicks from a pure strain of New Hampshire Red chickens homozygous for inherited muscular dystrophy. Fine structural studies of the musculus complexus in normal and dystrophic embryos were undertaken because of a sharp decrease in hatching by the diseased birds. Ultrastructural differences found between the normal and dystrophic embryos included a leached sarcoplasm, swollen and distorted mitochondria and tubular components, a lack of polyribosomes (myosin synthesis), and the formation of pseudostraps during differentiation of the myopathic hatching muscle. These differences may curtail differentiation until a point after the critical hatching time.