Muscle aims to consider aspects of the structure and function of selected muscle cells, primarily from vertebrates and arthropods, with the use of diagrams, light micrographs, and electron micrographs. The book begins by briefly tracing the historical development of studies on muscles. Pioneering studies established that while many cells show the property of contractility to a limited degree, muscle cells, whether striated or unstriated, are most obviously adapted to their function by hypertrophy of the fibrillar material rather than by acquisition of a unique set of cytoplasmic components. Separate chapters cover topics such as the striated muscle; the arrangement of myofibrils in striated muscle; the sarcomere and the molecular events of contraction; cytochemical demonstration of myofibrillar ATPase; and variation in the actin. Subsequent chapters deal with the functions of the mitochondria, nucleus, neuromuscular junction, plasma membrane, transverse tubular system, and sarcoplasmic reticulum. Also discussed are the cardiac muscle, smooth muscle, and muscle insertions.