This little book (first published in 1943 and re-issued with new introduction and bibliography is a useful reminder that human neuromuscular development is not a straightforward, simple, single-line graph but is the result of waves of motor development of different sorts occurring at different stages.
The work set out to attempt to correlate various motor activities in the infant with developmental observations in the cerebral tissue of infants. While this was not effectively accomplished the observations did point out that motor development goes through various stages with waxing and waning of different types of involuntary activity, which eventuate into well-integrated motor activity.