Complex sentence: From the time these bodies were buried up until the Middle Kingdom period, the dead were laid on their side, after this period they were buried on their backs (dorsal position) and from the Fifth Dynasty the bodies were always fully extended.
Split into simpler sentences: From the time these bodies were buried up until the Middle Kingdom period, the dead were laid on their sides. After this period they were buried on their backs (dorsal position), and from the Fifth Dynasty the bodies were always fully extended.