Penis bone (Baculum)
this penis bone (Baculum) is present in a wide range of species (not human) , however most of our closest relatives the primate possess a penis bone as do dogs, rodents and seals. It is located in the abdomen of the animal and when it is needed strong muscles push it out in to the erectile tissue it provides the penis with rigidity, adding in copulation, the size of this bone varies vastly among species, the walrus has a Penis bone of 30inch, (75cm) and some breeds of dog have a penis bone of 10cm and rodents are miniscule, the main function of this penile bone is to speed up the copulation process meaning the animal does not have to be in the vulnerable position of mating for any length of time, animals with out the bone must rely on the increase of blood pressure before copulation can take place, the picture depicts just a few of the different sizes and shapes of the Baculum over a number of different species (Softpedia, 2006)