On the Movement of Animals, Part One

although the fibers themselves are soft, they are not torn apart, but shorten spontaneously.

Individual fibers, after boiling, are inflated, and when inspected with a microscope, are seen to be little cylinders similar to the twigs of trees, which do not appear to be hollow tubes, as are reeds, but are seen to be full of a substance, or a certain pith, which must be spongy like elder wood. First, because any soft rod, which is inflated by an infused humor, swells and becomes straight, must necessarily be porous, since it is filled by aqueous granules as if by wedges, as is evident in a wetted rope.

Furthermore, the same thing is conjectured from the fact that in muscles saturated with blood and dried, as they are seen in ham with the help of a microscope, certain bloody droplets, or straight and transverse filaments, are seen in its fibers, separated from one another like porphyry stone; but this seems to be impossible if the internal substance of the fibers were not spongy.

Otherwise, the capillary vessels and nerves binding the prismatic bundles are more subtle than the columns or muscular fibrillae, which, however, do not exceed the thickness of a woman’s hair.

Finally, transverse ligatures do not seem to be made in the prisms, or muscular bundles, except loosely, since tendons, nerves, and membranes suffer no contraction when muscular fibers shorten and act. And this is evident in the anatomy of the living, and especially in the membrane of the diaphragm, which is corrugated while the included muscular fibers are contracted.