Where does “*natica” come from?

*natica (Vulgar Latin) comes from Latin natis, from Proto-Indo-European not- — rear, buttock.

Ancestry of “*natica”, step by step

Step	Language	Word	Meaning
1	Latin	natis	rump, buttocks; dative masculine plural of nātus;...
2	Proto-Indo-European	not-	rear, buttock