Sentence:  In February , 1959 , during the second admission to The New York Hospital , a biopsy specimen of the left <WSD>gastrocnemius</WSD> showed striking increase in the sarcolemmal sheath nuclei and shrunken muscle fibers in several sections . 
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