Sentence:  Microscopic studies of the gastrocnemius , pectoralis major , <WSD>transversus</WSD> 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:  a flat muscle with transverse fibers that forms the anterior and lateral walls of the abdominal cavity