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.