Complex sentence: The Bulgars had a special type of shamanic "medicine-men" who performed trepanations of the skull, usually near sagittal suture, not just symbolically, but also medically as in the two cases the patient had brain problems.
Split into simpler sentences: The Bulgars had a special type of shamanic "medicine-men" who performed trepanations of the skull, usually near the sagittal suture. This practice had medical application, as well as a symbolic purpose; in the two cases the patient had brain problems.