CAP. II. DE MUSCULI

—it follows that the aforementioned equal prisms are not equally long, nor equally thick; so that the one which is more oblique, ABDC, is longer and narrower than the one that is less oblique, AGHC. And therefore, the more the sides AB, CD are shortened, the more the thickness of the prism increases. Let us see now if the reasoning of these Illustrious Men coheres with the assumed principles and with experiments. When the prismatic fibers AB, CD are shortened and coincide with AG, CH, then the fibrous prisms must necessarily thicken, otherwise they would not fill the space. Therefore, the contracted fibers of the muscles become thicker, which is against their hypothesis.

Secondly, all fibers in a straight muscle parallel to each other are shortened. Therefore, lest there be a penetration of bodies, they must be inflated and thickened. And thus the thickness of the entire muscle must increase, which they likewise denied.

Thirdly, in the oblique intercostal muscle, the ribs are brought closer to each other, and all fibers are shortened at the same time, nor can their interstices be widened, since the obliquity of the fibers is rather increased. Therefore, the entire mass of the muscle will be diminished, which they also denied.

Finally, which is most important in this matter, is the mechanical reason by which the muscle moves a resistance by means of an organ. Furthermore, the constitution and disposition of the muscle, or rhomboid organ, seems most inept for raising the weight R. This could clearly and demonstratively be proven easily by those things which are to be exposed next; but, so that the doctrinal order is not disturbed, it will suffice to settle the matter with sensible experiments.

Let two equal wooden rules AC, BD be taken as in Fig. 6, TAB. I, and let them be connected by several equal threads AB, CD, etc., and let the end of the rod A be attached to a nail fixed in E, and to the end D let the weight R be applied. You will see, first, that once the rhomboid figure ABDC is destroyed, the rod BD is joined and drawn to the contact of the rule AC, so that out of them a single straight line AC, DR perpendicular to the horizon is formed.

And if the frequency and thickness of the intercepted ropes prevented the contact of the rods, a constricted and prolonged rhomboid would arise, Fig. 7, TAB. I, whose diameter ADF would extend to a position perpendicular to the horizon by oblique motion. The same thing will happen if the fibers AB, CD are consistent and flexible, like the twigs of trees; but in this case the rhomboid will retain a greater amplitude. Let us see now if, by shortening the ropes AB, CD, or by pulling them upwards, or by wetting them, the elevation of the ropes together with the hanging weight R follows. And we observe in Fig. 5, TAB. I, that in order for the adhesion and union of the rods BD & AC and the inclination of the entire rhomboid to be prevented, it is necessary that the rod BD be retained by transverse bonds or by transverse powers XZ pulling it. And then, with the ropes contracted, BD will approach towards AC by a motion equidistant to themselves; nor will the ropes ever be lifted around the center A towards AG as long as the rod BD is pulled downwards by the weight R. Wherefore, by means of a simple rhomboid muscle, the motive force of the fibers will not be able to raise the resistance R.

It is true, however, that in some cases the proposition can be verified, as if the fibers were attached to a firm bone EAC, Fig. 8, TAB. I, and the side of the rhomboid BD were retained in a smooth and slippery channel LF excavated in the column.