The penile bone and anterior process of the rat in scanning electron microscopy.

The penile bone and anterior process were made anorganic for scanning electron microscopy. The mature bone has a basal bulb and a long, cylindrical shaft bevelled at its tip to fit under a matching surface on the anterior process, giving rise to a bevelled 'suture'. A rough, resting, Sharpey-fibre bone surface covers the base and tip of the bone, the dorsal crest along the shaft, and parts of the lateral and ventral surfaces. The penile bone grows by endochondrial ossification at its basal end, but the cartilage cells are randomly disposed and not arranged in columns as in most 'long' bones. The growing bone, at 8 weeks, shows evidence of resorption externally where the base 'waists in' to the shaft: the corresponding endosteal surface within the basal bulb is formative, in accordance with the 'V-principle' of remodelling. It is concluded that the anterior process, penile bone and proximal erectile body (corpus cavernosum) form a firm, tightly fastened, articulating chain, perhaps serving to aid penetration.