Complex sentence: William Byrd Powell (1799-1867), a medical doctor and physiologist regarded the Atakapas as cannibals and noted that they traditionally flattened their skulls frontally and not occipitally--the opposite practice of neighboring tribes, such as the Natchez Nation.
Split into simpler sentences: William Byrd Powell (1799-1867), a medical doctor and physiologist, regarded the Atakapas as cannibals. He noted that they traditionally flattened their skulls frontally and not occipitally, a practice opposite to that of neighboring tribes, such as the Natchez Nation.