Scheme presenting the substructures of NGC 4438. It is based on the C-band image (see Fig. 1 and Sect. 5.1). The contours are at 3σ, 0.03 mJy, 0.08 mJy, 0.2 mJy, and 0.35 mJy. The orange line shows the hourglass-like structure mentioned in the Sect. 5.1. The NW side of the orange figure encloses the region referred to as the ‘base of the cone’. We name the circular cavity in the main bubble (blue circle) the ‘hole’.