If you think this is a femur, you're totally wrong!

It's a penis bone belonging to a cave bear!

The penis has a very simple job to do: to maintain sufficient stiffness to enter an orifice during the mating, and to deliver sperm. That's it.

Mammals solved it in the easiest way!

Most mammals have a unique bone called baculum (also penis bone, penile bone or os penis) in their penis. The only mammal species without baculum are the humans, horses, donkeys, rhinoceros, marsupials, rabbits, cetaceans (whales and dolphins), elephants and hyenas.

But baculum is present in most primates, rodents, carnivores, seals. The penis bone is kept in the abdomen and, when needed, a set of muscles push it into a sheath in the fleshy part of the penis.

It enters within the erectile tissue, providing rigidness to aid during the copulation. The penis bone varies in size and shape by species and its characteristics are sometimes used to differentiate between similar species.

The word baculum originally meant "stick" or "staff" in Latin. The homologue of the baculum in female mammals is known as the baubellum or os clitoris.

In humans and mammals lacking the baculum and baubellum, the rigidity of the erection is provided entirely through blood pressure in the corpus cavernosum. This bone aids in copulation when mates have only a short encounter and need to perform quickly.

The baculum is for speed: sliding a bone in and out of a sheath is much faster than waiting for the hydraulics to kick in and limits the time spent mating, which is, after all, in a vulnerable position.

Indeed, mammals without a baculum have in change larger erectile penises and they perform much longer during copulation! ....

The baculum explains lion's sexual marathon of roughly 250 copulations in 4 days, even if each copulation lasts 30-70 seconds ....Because, in this case, erection depends more on a willingly moved muscle and not in tissue turgescence.

The largest baculum in the mammal kingdom belongs to the walrus, which can reach a length of 30 inches (75 cm): as big as a human femur!

Even large dogs have a 10 cm baculum!

Throughout many cultures, the penis bone has been used in rituals and is believed to possess the power and virility of the animal to which it once belonged.

In Chinese traditional medicine, tiger and bear bone penises are considered aphrodisiacs!

Unfortunately, this provoked a great deal of poaching in these animals, putting these species on the brink of extinction! ....

In the Bible's Book of Genesis, Adam's rib is removed to create Eve. Old Hebrew does not have a word for penis.

Some scholars suggest this story is an explanatory myth to explain the absence of a baculum in the human male, rather than a missing rib (in light of the fact that men and women have the same number of ribs).