II. On some elementary principles in animal mechanics. —No. V. On the most perfect form of a plane quadrilateral muscle connecting two bones

Let us suppose two bones, AB and A'B', lying in the same plane, joined by muscular fibres, and any two planes drawn through these bones intersecting in a line PQ. If we suppose one bone AB to be fixed and the other bone A'B' to be movable, and that the contraction of the muscle compels the bone A'B' to revolve round PQ as an axis of rotation, it is required to find the conditions necessary in order that the work done by the contraction of the muscle shall be a maximum. I shall in this note discuss only the case in which the bones AB, A'B' lie in the same plane. In this case I have succeeded in demonstrating the following propositions in the case of maximum work:— 1. The axis of rotation PQ must be formed by the intersection of rectangular planes passing through AB and A'B'.