They may have neglected to list the stitch holder, but they want you to work up to the humps and then work each hump one at a time. If you don't have a big enough holder, you can leave one hump on a spare needle or run a strand of yarn through the stitches.
Once you have one side 'on hold' you follow these directions:
On these 17 sts only, knit one row, purl one row.
Start decreasing. *
Next row, K 2 tog, knit across, to last 2 sts, k 2 tog.
Purl next row.
Repeat these last 2 rows until there are 7 sts remaining, ending on the last decrease row of k 2 tog each end. * Bind off on purl side row.
Then you put the other side back on the needles and follow the directions for the second hump.