Complex sentence: The plate curved around the torso and ended near the armpits, held in place and adjusted to a snug fit by shoulder straps that crossed the back, forming an X-shape, and was secured with hook-and-eye closures.
Split into simpler sentences: The plate curved around the torso and ended near the armpits. This was held in place and adjusted to a snug fit by shoulder straps that crossed the back, forming an X-shape, and was secured with hook-and-eye closures.