by the magazine, but it'd definitely be very awkward - you can't really wrap your hand around that, I guess you'd need to basically have your thumb sort of resting along the side, which probably isn't going to be very comfortable, especially with the weird angle your hand would have to be sitting in
(on this C96 Mauser that grip is used to avoid having the hammer smack right into the webbing of your hand, which is occasionally a problem on some pistols, but particularly on the Mauser with the stock attached)