Paper - The development of the musculature of the body wall in the pig (1900)

From Embryology

Bardeen CR. The development of the musculature of the body wall in the pig Johns Hopkins Med. J 9: 367-400.

XVI. The Development of the Musculature of the Body- Wall in the Pig

including its Histogenesis and Its delations to the Myotomes and to the Skeletal and Nervous Apparatus.

By Charles Bussell Bardeen, M. D.,

Associate in Anatomy, The Johns Hopkins University.

With 10 plates. Pages 367 to 399.

The investigation considers the development of the intrinsic thoraco-abdominal musculature from the myotonies in the pig's embryo. The histological changes taking place in the musculature are described, as well as the early relations of the musculature to the nervous and skeletal apparatus.

Three periods are recognized in the development of the musculature:

1. The period during which the myotomes expaud dorsally and send ventral processes into the membrana reuniens. The cells, both of the mesial and the lateral plates of the myotomes are shown to lie converted into musele-tissues.

2. The period during which the tissue of the myotome, becomes utilized in the formation of the muscles characteristic of the adult. Segmentation is shown to persist only where the muscle-tissue remains throughout united to the vertebras or to the ribs. The peripheral nerves are shown to develop independently of the myotomes, and to become associated directly with the musculature only after the muscles have become differentiated.

3. The period during which the muscles expand, become perfected in internal structure and are shifted into the relative positions characteristic of the adult.

Cell-multiplication takes place during the first two periods and during the early part of the third. Cell-division takes place by mitosis in round undifferentiated "myoblasts." From these the muscle-cells are developed by elongation of the cell-body, nuclear multiplication by direct division, and fibrillar differentiation of the protoplasm. The differentiated muscle-cells do not divide to form new cells. During the third period, however, many of the muscle-cells undergo retrograde metamorphosis.