How to cast on in the middle of a row?

[knitnnpurln]

Can someone please explain to me how to cast on in the middle of a row? I'm making Peek-A-Boo mittens (opening in the middle of the palm to get fingers out of). I've completed the first one but the cast on edge looks horrible!!!!!!

knitnnpurln

[suzeeq]

Use a knit or cable cast on. Swap the right needle into the left hand, cast on the sts, then put it back into the right hand. Knit the sts on the next round.