Figure 1.

(a) A photograph of a bluegill sunfish. (b) Schematic showing the location of the fish fins. The pectoral fin is highlighted with the blue box. (c) A photograph of a cleared and stained pectoral fin. The short segments can be seen along the length of the rays. (d) Schematic showing dorsal views of a fin ray with two hemitrichs. Muscles (not shown) exert forces on the tendons attached to the head of each hemitrich. (e) Single cross-section slice from a microCT scan of a pectoral fin. The upper panel shows multiple rays and the lower panel shows an expanded cross-section of two rays. Each of the two rays is composed of two hemitrichs. The bright white regions are bony areas and the grey is softer tissues (fin membrane and connective tissues). The separation between the two hemitrichs of the left ray is labelled ‘dist=d’. (f) Apparatus for holding ray hemitrichs. The ray (label ‘i’) is held by two clips (label ‘ii’). The upper clip can move to apply an offset between the hemitrichs. The inset image shows the end-on view. The upper clip holds one hemitrich and the lower clip holds the other hemitrich.