We asked exactly the same question about max (11months) a few months ago on COL, you could feel his ribs and in certain positions you could see them.
As said earlier on, we found increasing Burns gives max the runs, and the vet did have a look at him and said he's a very active dog with a high metabolism, and not to worry.
Again the vet suggested we could give a third meal.
As recomended to us by people on here we gave max more tripe, and increased his meat, so now hes mostly on barf with the occasional Burns meal. Max has more than the recomended amounts and although he has gained some weight he is still a fairly skinny dog. ( or well defined )
We don't worry to much about it any more as he is very fit and healthy. It may also be hormonal, and the weight will be gained when he's older.
On looking at Max he looks only slighty more filled out than Teddy, but not much .Max at 11 months weighs 14kg and he is a long leggy dog.