On the Movement of Animals, Part One

versely, the retraction of that joint to whose boundary the muscle had been attached ceases entirely, while in the meantime the action of the same joint remains unimpaired, which depends on other muscles ending there.

Likewise, it is known that a muscle is a machine inert and dead in itself, unless a motive faculty comes from without, which brings command and excites it from sleep and torpor, and impels it to motion; because, naturally, in sleep and rest, the muscle of the elbow, for example, even though it be whole and uninjured, does not move the arm unless it is impelled by the appetite to exercise action.

But it has been asked hitherto by what path and through what conduits the command of the soul and the motive faculty are carried to the muscle. This, however, sense and experience have easily revealed. For when arteries, veins, and nerves are led from the outside to the muscle, our predecessors proved by this reasoning that this duty is not owed to the veins or the arteries: for if a vein or artery had been tied or severed, the motive faculty should not have been carried to the muscle—the passage and way being closed or removed—and yet it was observed that the muscle exercises its motions no less than it did when the aforementioned vessels were intact. Whence it is gathered that the motive faculty is not transferred through veins or arteries to agitate the muscle. On the contrary, when the nerve that terminates and is inserted into a certain muscle is severed or tightly ligated, the movement and agitation of that muscle cease entirely, and it remains completely inert and immobile like a corpse. Wherefore, the nerve is the conduit through which the motive faculty is communicated in order to excite, move, or convey—if I may say so—the command of the appetite to the muscle, so that it may be moved and agitated. But what indeed is carried through the nerves to the muscle? Whether it is the motive faculty incor-