This stitch is similar to the fishbone stitch, with a requirement to divide the pattern into two. The difference is that the stitches in the centre of the pattern does not fall on the stitch line, but on its either sides. This helps to make the stitches far spaced to create the open fishbone effect.

It is good to know the fishbone stitch to understand this stitch. I will work on a leaf shaped pattern. I have marked the centre with a stitch line. The lines are named X, Y and Z for the ease of the lesson.

opened_fishbone_stitch_1      opened_fishbone_stitch_2
Fig 1: Like in fishbone stitch, first, bring out the needle through A, which is the top tip of the leaf. Take it in through B, a point on line Y. Then, bring it out through C, a point on line X.
It is not essential to do the stitch A-B. You have the option of starting the stitch from the point C.
  Fig 2: Now, put in the needle through D, which is a point just outside the line Y. Bring out the needle through E, a point on line Z.
opened_fishbone_stitch_3   opened_fishbone_stitch_4
Fig 3: Follow this pattern of stitching alternatley on the lines X and Y. Be careful that no stitch will fall on the line Y, but only on its either sides.   Fig 4: A completed leaf pattern will look like this.