Prolonged paralysis of the chick embryo, with special reference to effects on the vertebral column

Chick embryos were paralysed with decamethonium, the first dose usually being administtered at 5 days of incubation. Some of the specimens were kept paralysed for as long as 1 week. A number of the treated embryos exhibited deformations in the shape of the body or abnormal postures of the limbs. These features were probably caused by pressures arising from contact between the embryo and the actively contracting amniotic membrane. In transverse sections through the thorax of some of the embryos, the vertebral column was seen to have been rotated about its axis. The rotation, as viewed from the anterior aspect, was always in an anticlockwise direction, and the mid-sagittal plane of the vertebral column was at an angle of about 30-40 degrees to the median plane of the body. In longitudinal sections, the vertebral column was sometimes found to be buckled into an S-shaped curvature, presumably as a consequence of anteroposterior compression of the body, which could not be compensated for because of the muscular paralysis. There was extensive cartilaginous union between the vertebrae, and the articulation of the first cervical vertebra with the skull was also fused. The results obtained by paralysis indicate that functional activity of the embryonic skeletal musculature plays important roles in ensuring normal development; firstly, by enabling the embryo to resist external mechanical pressures which would otherwise result in a distortion of its shape, and secondly, by being a causal factor in the formation of movable articulations within the vertebral column