Sentence:  For this asymptotic case we are considering, k - r \, and  - (54), is the distance from the apex multiplied by some constant factor Fig 4 shows that the <WSD>crosswedge</WSD> wavelength decreases as the wave approaches the apex. 
Meaning of the word marked with <WSD> tags:  A wedge-shaped waveform that moves in the cross direction to the current.