Section 96. We Have, in the Skeleton, a Complicated Apparatus of

parts hinged and movable upon one another; the agent moving these parts is the same agent that we find in the heart walls propelling the blood through the circulation, in the alimentary canal squeezing the food along its course, and universally in the body where motion occurs, except in the case of the creeping phagocytes, and the ciliary waving of ciliated epithelium. This agent is muscle. We have, in muscular tissue, a very wide departure from the structure of the primordial cell; to use a common biological expression, a very great amount of modification (= differentiation). Sheet 7 represents the simpler kind of muscular tissue, unstriated muscle, in which the cell character is still fairly obvious. The cells are fusiform (spindle-shaped), have a distinct nucleus and faint longitudinal striations (striations along their length), but no transverse striations.