Casting On while knitting in the round?

I am currently making a dog sweater. I have been knitting in the round for a while but the pattern calls for me to start the next row by K2, CO4, knit until the last 6 sts, CO4 and K2. How do I cast on in this case (in the middle of the project)?

Use a knit or cable caston. Put the right needle into the left hand, cast on with the working yarn, then switch it back to the right hand and knit the rest of the sts.

Thanks for the help. But I think now I have confused myself even more, although your cast-on advice helped I think I may be doing something wrong. The part of the pattern that I need help with goes like :

Continue alternating stockinette stitch and the increase row until you have reached 44 stitches ending with a knit row.
To make leg openings:
Next round: K2, CO4, knit to last 6 sts, CO4, K2.
K2, (leg opening is here), break yarn leaving a LONG tail (you will be using this to knit the stitches between the leg openings – approx 4 -5 feet should be fine), rejoin main ball to the next stitch and K32, turn (you will be at next leg opening), P32, P4 between leg openings (using little ball), turn, K4, K32 (using main ball), turn, P32, P4 (using little ball), K2 (you will be at beginning of round).

It also says that if I want to make the sweater for a smaller dog I should:
If you’re knitting for a smaller dog, knit this on U.S 7-8 needles and increasing the stitches between legs to 6-8 total instead of 4.

Does CO in this case stand for cast off? because it appears as if CO4, K2 goes towards the 6 sts I have left. Where should I be adding in the extra stitches?

That is a little confusing. Usually CO means cast on but if they use the term ‘cast off’ it[I] could[/I] mean that. But it should either mean one or the other not both. Do they have an explanation of their abbreviations anywhere with the pattern (book, site or whatever)?

Next round: K2, CO4, knit to last 6 sts, CO4, K2.
The first thing that occurs to a person is that they want you to cast on, but that last part, like you say seems to refer to 6 stitches and would have to be cast off. So it should mean that in both instances. I don’t see where it tells you to cast back on over those 4 stitches you cast off but you probably do somewhere. It would be like a large buttonhole. You probably bind off four and then cast them back on on the other side. Does it seems that that could be right?

That is confusing. Most people would see CO as cast on, and write out Cast Off if that is meant or use BO/bind off instead. I wondered if there had been a bind off on the previous row…

So yep, you bind off 4 sts, knit to the end of the row, bind off another for and knit 2. Then you will be using separate strands of yarn to knit the main body and probably those k2 sts at the ends, then will rejoin later probably with a cast on.