Is it normal that i have a dip at the base of my skull?

It's been there for quite a while. I just thought about it again. I rub my hand down the back of my head down to my neck, and it dips in. Next to it, on both sides, my skull just merges with my neck. No bumps/dips nothing. I was just wondering if anyone else has this? I haven't had any injuries there either. But I do have arthritis in my neck.