De Motu Animalium

effects those first externæ motiones external motions, some things must be posited which the evidence of the senses demonstrates. Truly, that the principium & causa effectiva motûs animalium principle and effective cause of the motion of animals is the anima soul, no one certainly ignores, since living things live through the soul, and during life motion persists in them. But when the animal is extinct—that is, the soul no longer operating—the animal machine is left entirely inert and immobile.

That the manifold and numerous motiones motions of an animal are made by electione choice, or by a certain naturali appetitu natural appetite of the animal, this also is admitted by everyone as most evident.

It is also manifest that cognition and appetitus appetite do not, of themselves alone, move and impel the parts of the animal, but have need of the necessary instruments, without which motus motion cannot be effected.

They commonly distinguish the instrumenta motûs instruments of motion; for they wish one to be activum active, and another organicum organic and merely passivum passive. The instrumentum animæ activum active instrument of the soul is usually called virtus power, or facultas loco motiva locomotive faculty; however, this is commonly thought to reside in the spiritibus animalibus animal spirits.

Regarding the organum immediatum immediate organ by which the facultas motiva motive faculty of the soul moves the parts of the animal, according to ARISTOTLE, these are merely the spiritus spirits, which flow from the heart through the arteries into the extremitates nerveas nervous extremities, terminating and degenerating, extending even to the flexures of the same joints; they move the bones by drawing them toward themselves, as often as the joint is flexed, or by pushing them outward, as often as the joint is extended. But this doctrine is rejected by GALEN, and by all others, and by the evidence of the senses itself, by which it is established that musculi muscles are the organs and machines by which the motiva motive faculty of the soul moves the joints and parts of the animal.

This has long been confirmed, because when musculi muscles are cut transversely, the retraction of that joint to