Some cricket pitches have an additional white line, perpendicular to both the bowling crease and popping crease, and joining both of them. One example is of the Eden Garden stadium pitch (2016)
I have highlighted the line in question in a pink box. There are three more lines, a total of two on each side of the pitch. I checked Law 7 - The Creases and Law 6 - the Pitch, and could not find any reference to these lines.
What are they? Are they not standard lines i.e. why are they not on every pitch? What is their purpose?