Next to the two grand Acts of animal Life, their Sense or Respiration, I shall consider their Motion, or locomotive Faculty; whereby they convey themselves from Place to Place, according to their Occasions, and Way of Life: And the admirable Apparatus to this Purpose, is a plain Demonstration of God’s particular Foresight, Care, and especial Providence towards all the animal World.
And here I might view in the first Place the Muscles, their curious Structure[a], the nice tacking them to every Joynt, to pull it this Way, and that Way, and the other Way, according to the special Purpose, Design, and Office of every such Joint: Also their various Size and Strength; some large and corpulent, others less, and some scarce visible to the naked Eye; all exactly fitted to every Place, and every use of the Body. And lastly, I might take Notice of the muscular Motions, both involuntary and spontaneous[].
Next, I might survey the special Fabrick of the Bones[c], ministring to animal Motion. Next, I might take notice of the Joynts[d], their compleat Form adjusted to the Place, and Office they are employed in; their Bandage, keeping them from Luxations; the oily Matter[e] to lubricate them, and their own Smoothness to facilitate their Motion.
And lastly, I might trace the various Nerves throughout the Body; sent about to minister to its various Motions[f]. I might consider their Origine[g], their Ramifications to the several Parts, and their Inosculations with one another, according to the Harmony and Accord of one Part with another, necessary for the Benefit of the Animal. But some of those Things I have given some Touches upon already, and more I shall mention hereafter[h], and it would be tedious here to insist upon them all.
I shall therefore only speak distinctly to the Locomotive Act it self, or what directly relates to it.
And here it is admirable to consider the various Methods of Nature[], suited to the Occasions of various Animals. In some their Motion is swift, in others slow. In some performed with two, four, or more Legs: in some with two, or four Wings: in some with neither[k].
And first for swift or slow Motion. This we find is proportional to the Occasions of each respective Animal. Reptiles, whose Food, Habitation, and Nests, lie in the next Clod, Plant, Tree, or Hole, or can bear long Hunger and Hardship, they need neither Legs nor Wings for their Transportation; but their vermicular or sinuous Motion (performed with no less Art, and as curiously provided for as the Legs or Wings of other Creatures: This, I say,) is sufficient for their Conveyance.
Man and Beasts, whose Occasions require a large Room, have accordingly a swifter Motion, with proper Engines for that Service; answerable to their Range for Food, their Occupation of Business, or their want of Armature, and to secure them against Harms[l].
But for the winged Creatures (Birds and Insects,) as they are to traverse large Tracts of Land and Water, for their Food, for their commodious Habitation, or Breeding their Young, to find Places of Retreat and Security from Mischiefs; so they have accordingly the Faculty of flying in the Air; and that swiftly or slowly, a long or short a Time, according to their Occasions and Way of Life. And accordingly their Wings, and whole Body, are curiously prepared for such a Motion; as I intend to shew in a proper Place[m].
Another remarkable Thing in the motive Faculty of all Creatures, is the neat, geometrical Performance of it. The most accurate Mathematician, the most skilful in mechanick Motions, can’t prescribe a nicer Motion (than what they perform) to the Legs and Wings of those that walk or fly[n], or to the Bodies of those that creep[o]. Neither can the Body be more compleatly poised for the Motion it is to have in every Creature, than it already actually is. From the largest Elephant, to the smallest Mite, we find the Body artfully balanced[p]. The Head not too heavy, nor too light for the rest of the Body, nor the rest of the Body for it[q]. The Viscera are not let loose, or so placed, as to swag, over-balance, or over-set the Body; but well-braced, and distributed to maintain the æquipoise of the Body. The motive Parts also are admirably well fixed in respect to the Center of Gravity; placed in the very Point, fittest to support and convey the Body. Every Leg beareth his true Share of the Body’s Weight. And the Wings so nicely are set to the Center of Gravity, as even in that fluid Medium, the Air, the Body is as truly balanced, as we could have balanced it with the nicest Scales.