when you say you split the lips is it to this that you are referring ?
split =
The operation of cutting a hide or skin horizontally into two or more layers, e.g. a grain and a flesh layer.
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That's loose terminology. Many times, in remote field sites, lips are split as you described and salted to prevent the hide from spoiling. In our jargon, however, it is removal of all the flesh between those layers of skin in the lip. All vestiges of flesh must be removed to prevent "lumps" when the mounting is completed as well as removing a source of insect infestation.
Take your own bottom lip and feel it, the whole thing right to where it goes up to the jaw bone inside your mouth. It is very fleshy because there are muscles in it that move your lips. This area has to be opened up and the muscle tissue removed so that the salt can get to the skin on both sides, the lip skin outside and inside your(the animal's)mouth. Opening up this lip "fold" is called splitting the lips. The same is true of eyelids, they are folds of skin that need to be opened up.
both of you
it helped
yasmine