2. Functions of the Muscular System.
2686. The muscular system performs, in an active sense, what the osseous system does in a passive. The strength or power of the muscles, and their leverage attachment, is here especially to be regarded. The contraction of the fibres is a charging, by nerves and blood, of the two fibre-poles.
2687. The fibres are charged by the air. It is, in the most general sense, the respiratory vessels by which the muscle is charged. This is strictly the case in Insects, where the tracheæ traverse all the limbs, and directly conduct to the flesh the polarity of the air. In animals, however, with a closed circulation, the arteries undertake the conveyance of air upon the blood, and it is then the latter fluid which streams into the muscles in order to charge them.
2688. Thus if an artery be ligatured, the limb is crippled or lamed. The artery, however, imparts only the positive pole, and consequently of itself produces no shortening or contraction of the fibres. The oxydation takes place at the lower end of the muscle; here, therefore, the latter passes over into tendon.
2689. The nerve is the second condition of the muscular contraction, since it evokes in the fibre the negative pole. Thus if a nerve be ligatured, the limb is likewise motionless.
2690. If the poles be brought by contraction into close approximation, the fibres must re-extend, so soon as the influence of the blood or the nerve ceases.
2691. Now since the blood is constantly streaming in, the reason for the muscular rest must reside in the nerves. The rationale of voluntary motion is consequently the nerve. The relaxation or extension is an unloading of the fibres.
2692. The muscular motion is an electrical process, a motion of blood in the Solid.
2693. Through the polarization of the fibres the muscle is formed from the arteries. The muscle is therefore an individual biconical piece of fibre, having unequal cones. Oxydation takes place at the muscular extremity; here, therefore, originates the sinew or tendon.
2694. A fleshy cyst—or heart—which includes an osseous cyst, must subdivide into several fibrous cones or muscles. One reason of this is the "fore and aft," another is the quantity of the essential vascular branches.