Sentence:  Microscopic studies of the <WSD>gastrocnemius</WSD> , pectoralis major , transversus abdominis , biceps brachii , and diaphragm showed atrophy as well as varying degrees of injury ranging from swelling and vacuolization to focal necrosis of the muscle fibers . 
Meaning of the word marked with <WSD> tags:  the muscle in the back part of the leg that forms the greater part of the calf; responsible for the plantar flexion of the foot