Cover Image Explanation

This pictures show penis bones from a ferret, rat, and mouse. The samples are stained using a Von Kossa stain, which turns mineralized tissues, like bone, black while the unmineralized tissue is counter stained to be blue for contrast. You are looking at these bones from a side view, and all of the specimens are cut down the midline along their long axis. The right hand side of the image is closer to the animals body, and the left is the tip of the penis. This image truly illustrates how different penis bones can be across species. Below are some finer points that I want to highlight. 1) The ferret penis bone has an exaggerated curvature, which is not uncommon in carnivoran penis bones. 2) The rat penis bone has two distinct mineralized regions, and the one closer to the tip of the penis is most likely calcified cartilage, the one on there right is endochondral bone. 3) The medullary cavities, observed as the open space in the bones, are of very different sizes between the three species. This may tell us something about the functional biomechanics of all three penis bones.