[Variants of congenital hypoplasia of the arches of the upper cervical vertebrae and their clinical significance].

A clinico-roentgenological examination of the transitional craniovertebral division has revealed a high incidence and a great diversity of isolated underdevelopment of the arches of the upper cervical vertebra--from their fissure-like splitting to complete absence. Usually these forms create no preconditions for disturbances of any functions, do not manifest clinically, and can be regarded as variants of normal structure of the craniovertebral division.