On the Movement of Animals, Part One

Others consist of fibers wound around like a ball of thread, and are called circular-spirals.
I have also seen in the tail of a lobster muscles interwoven not like cloth, but composed of bundles of complicated fibers, as the hair of women is accustomed to be arranged.

PROPOS. IV.

a Tab. 1. Fig. 1. 2. 3. 4.

In a muscle, we see that only the fleshy filaments AB, CD, EF, & C of the same figures a are shortened when the muscle acts; the terminal tendons BH, to which the fleshy fibers are fastened, are not contracted, but retain the same length that they previously had; this sense is evident in the anatomy of living creatures.

Hence it follows that only the fleshy fibers AB, CD, EF, GN, & C exert force by suspending huge weights through the energy by which they are contracted. The tendons BH, however, suffer force insofar as they are pulled by a simple local motion by the contracted fleshy threads, and serve them like handles, to which the fibers are fastened.

PROPOS. V.

In these last years a new idea has been put forth concerning the true form of a muscle, and its mechanical mode of operating, concerning which, for the love of truth, we shall set forth our opinion. Tab. 1. Fig. 5. 6. 7. & 8.