Muscle seperation between bicep and tricep

Not sure if it matters, but I am currently on a bulk. All my excess fat is going to my belly and not my arms which might or might not be a good thing. Anyways at the moment when I open my arms up as if I am going to give my car a hug I can see a gap between my bicep and my tricep on the inside of my arm; it gets more pronounced when I flex. When I do a front double bicep pose I see the same thing. It looks like a line across my arm is caved in. Is this something I should be worried about? Like say my tricep is underdeveloped or something? Are there any exercises I could do to fix this if it is something I need fixing? Thanks for any help.

Bump.

Pics?

This same thing is currently happening on my right arm. I have no idea what it means. I don't know if it's dangerous, or if it's just something I'm doing wrong (not working out certain muscles in that area?). Would love to hear what others have to say about this.