sentences:  This also occurs in babies under c. 1 year, because of low myelination of the corticospinal tracts.As these tracts develop to adult form, the flexion-reflex circuit is inhibited by the descending corticospinal inputs, and the normal plantar reflex develops.The Babinski reflex is a sign of neurological abnormality (e.g., upper motor neuron lesion) in adults.