"The human machine: The anatomical structure & mechanism of the human body" by George Brant Bridgman

IT appears to be a fixed law that the contraction of a muscle shall be toward its centre, therefore, the subject for mechanism on each occasion is so to modify the figure, and adjust the position of the muscle as to produce the motion required agreeably with this law. This can only be done by giving to different muscles a diversity of configuration suited to their several offices and to their situation with respect to the work which they have to perform. On which account we find them under a multiplicity of forms and altitudes; sometimes with double, sometimes with treble tendons; sometimes with none, sometimes with one tendon to several muscles; at other times with one muscle to several tendons. The shape of the organ is susceptible of an incalculable variety, while the original property of the muscle. The law and line of its contraction
remains the same and is simple. Herein the muscular system may be said to bear a perfect resemblance to our works of art.
An artist does not alter the native quality of his materials or their laws of action. He takes these as he finds them. His skill and ingenuity are employed in turning them such as they are, to his account by giving to the parts of his machine a form and relation in which these unalterable properties may operate to the production of the effects intended.