Any Idea What These Lines Are On 1851 Large Cent?

They are left over die scratches. Die scratches in the open field area flatten faster than die scratches next to devices. They they are surrounded with a devices (like inside a device or mint mark) they will last a lot longer. Note how the die scratch fades to flat when it get further from a device. This is a good thing, because an older die scratch you maybe look for, is often found closest to a device. So remember this when searching for die scratches as a marker for a die state. If they are faded, then they are a later die state than one with stronger die scratches. Hope this helps.