The 21-cm line intensities in a (Z, R) distribution is studied at the locus of tangential points of the inner parts of the Galaxy using both Northern and Southern data. A corrugation effect is observed in the galactic neutral hydrogen layer with an average wave length of 2 kpc and a wave amplitude of 70 pc. The patterns obtained for the I and the IV quadrant indicate that the inner and the outer parts of the spiral arms are located, respectively, below and above the galactic plane. Also, with high angular resolution the corrugation pattern suggests the existence of ‘faults’ in a geological sense in the inter arm zones. Optical studies of spatial distribution of early objects show good agreement with the neutral hydrogen results, indicating that the observed corrugation pattern is an indication of real distribution of matter in the galactic layer, and not of a kinematical effect.