A phenomenon discovered by Vorontsov-Vel’yaminov — straight segments in the spiral structure of giant galaxies — is studied. The main geometrical and physical characteristics of these structures are demonstrated using the example of the galaxies M101 and especially M51. It is shown that rows alternate with regular spiral arms over almost their entire extent in M101, M51, and a number of other galaxies. The relationship between rows and straight warm dust lanes at the inner edges of spiral arms is traced. Assuming these dust lanes to be gas layers compressed by a spiral shock wave, the possibility that rows are formed in local segments of the spiral shock front that are being flattened is discussed. New observational facts about rows support the quantitative consequences of this gasdynamical picture.
