If somebody is knowledgeable about this area of biology I would really like to understand the details better.

I know with canines the erection begins with the baculum being pushed out and the erectile tissue only comes into play later. But what pushes it out? Muscles? Voluntary or involuntary ones? I suppose when not erect the bone must be resting inside the body somewhere near the sheath. Is there some kind of a channel where it is free to move back and forth?

What about other species with penis bones? Are they the same as canines?

supina said:
If somebody is knowledgeable about this area of biology I would really like to understand the details better.

I know with canines the erection begins with the baculum being pushed out and the erectile tissue only comes into play later. But what pushes it out? Muscles? Voluntary or involuntary ones? I suppose when not erect the bone must be resting inside the body somewhere near the sheath. Is there some kind of a channel where it is free to move back and forth?

What about other species with penis bones? Are they the same as canines?

"Most mammals have a bone that regulates penis extension. Called a baculum, penis bone, or os penis, this bone is normally kept in the abdomen of the male and, when needed, a set of muscles contract and push it into a sheath within the penis. It enters the erectile tissue, providing stiffness to enable entry and sperm deposition in the female reproductive tract" (Wessel, 2012).

thegreatwolfgang said:
"Most mammals have a bone that regulates penis extension. Called a baculum, penis bone, or os penis, this bone is normally kept in the abdomen of the male and, when needed, a set of muscles contract and push it into a sheath within the penis. It enters the erectile tissue, providing stiffness to enable entry and sperm deposition in the female reproductive tract" (Wessel, 2012).

Thanks, that answers some of my questions. You don't happen to know if the bone is complitely free or attached to some kind of strechy connective tissue?

supina said:
Thanks, that answers some of my questions. You don't happen to know if the bone is complitely free or attached to some kind of strechy connective tissue?

Bone is just inside the penis, then the penis tissue inflates around it. So when fully flaccid, you basically see the shape of the bone.

I'm not 100% sure as i didn't really look into it that close, but the way understand it is that it covers about 80% of the penis length, that would be from the knot to about almost the tip, the area where we have the glans.
And up to the knot because any further and they wouldn't be able to turn around - rotate that tissue behind it when they go ass_to_ass.

And a pic showing it

supina said:
Thanks, that answers some of my questions. You don't happen to know if the bone is complitely free or attached to some kind of strechy connective tissue?

If you are asking whether it is connected to the rest of the skeleton, multiple sources have stated that the bone is separate from the axial and appendicular skeleton, developing within the soft organ itself (Bhavya, n.d.; Brindle, 2016; Colville, 2010 ).

As for whether or not the bone is in any way connected to the organ, results vary between species. A study on rats found that "there are neither muscular nor ligamentous connections between the baculum and the corpus cavernosum, and there is very little overlap of the corpus cavernosum onto the external surface of the baculum in flaccid penises" (Kelly, 2000) while another study on bobcats found that "the connection between the baculum and corpus cavernosum is characterized by the insertion of collagen fibres originating from the tunica albuginea deep into the bone" (Tumlison & McDaniel, 1984, as cited in Brassey et al., 2020 ).

thegreatwolfgang said:
If you are asking whether it is connected to the rest of the skeleton, multiple sources have stated that the bone is separate from the axial and appendicular skeleton, developing within the soft organ itself (Bhavya, n.d.; Brindle, 2016; Colville, 2010 ).

As for whether or not the bone is in any way connected to the organ, results vary between species. A study on rats found that "there are neither muscular nor ligamentous connections between the baculum and the corpus cavernosum, and there is very little overlap of the corpus cavernosum onto the external surface of the baculum in flaccid penises" (Kelly, 2000) while another study on bobcats found that "the connection between the baculum and corpus cavernosum is characterized by the insertion of collagen fibres originating from the tunica albuginea deep into the bone" (Tumlison & McDaniel, 1984, as cited in Brassey et al., 2020 ).

Wow, where do you find that stuff? Google Scholar?

Now the only question I still have is if that pushing out is voluntary or involuntary. So if we have an anatomically accurate anthro would he be able to control when the bone comes out or would it be as much out of their control as human erection? I know this is probably a bit harder question as we can't exactly go and ask animals about this.

supina said:
Wow, where do you find that stuff? Google Scholar?

Or just by simply googling keywords, these are just some things you pick up by doing academic research.

Now the only question I still have is if that pushing out is voluntary or involuntary. So if we have an anatomically accurate anthro would he be able to control when the bone comes out or would it be as much out of their control as human erection? I know this is probably a bit harder question as we can't exactly go and ask animals about this.

While Wessel (2012) did state that "a set of muscles contract and push it into a sheath within the penis", I can't figure out what specific set of muscles or species are involved.
Other studies have found that the baculum just floats at the tip of the penis, relying more on the expanding corpus cavernosa to "extend" them (like the tip of an expandable baton).
Since the baculum is contained within the penis itself and that there are no muscles connected, I would think it's safe to assume that it extends alongside the penis during erection.
Just like how humans can have penile implants to help them with erectile dysfunction, some animals naturally have them to help support their erections for survival and evolutionary purposes.

So to answer your question on anthros, it is irrelevant whether or not they can control it. The bone does not "come out" as it's already embedded within the penis. The question is whether or not they can control their own erections.

thegreatwolfgang said:
While Wessel (2012) did state that "a set of muscles contract and push it into a sheath within the penis", I can't figure out what specific set of muscles or species are involved.
Other studies have found that the baculum just floats at the tip of the penis, relying more on the expanding corpus cavernosa to "extend" them (like the tip of an expandable baton).
Since the baculum is contained within the penis itself and that there are no muscles connected, I would think it's safe to assume that it extends alongside the penis during erection.
Just like how humans can have penile implants to help them with erectile dysfunction, some animals naturally have them to help support their erections for survival and evolutionary purposes.

So to answer your question on anthros, it is irrelevant whether or not they can control it. The bone does not "come out" as it's already embedded within the penis. The question is whether or not they can control their own erections.

That's seemingly contradictory with what was written above. Sure, for species with just small baculums it would be like this. But as we know for canines at least the bone alone can hold the erection so its extension can't rely on the corpus cavernosa. And if it "is normally kept in the abdomen of the male" how can it also be embedded within the penis? Moreover, aren't the sheaths of many animals a lot shorter than the erect penis? Or are these all species with small baculums?

supina said:
That's seemingly contradictory with what was written above. Sure, for species with just small baculums it would be like this. But as we know for canines at least the bone alone can hold the erection so its extension can't rely on the corpus cavernosa. And if it "is normally kept in the abdomen of the male" how can it also be embedded within the penis? Moreover, aren't the sheaths of many animals a lot shorter than the erect penis? Or are these all species with small baculums?

It's important to understand that baculums (or bacula) are not the same across every species. Therefore, it wouldn't be safe to generalise everything we know based on that one article.
I see their statement of the baculum being "normally kept in the abdomen" and later having "muscles contract and push it into a sheath" as being indicative for the unknown number of species they had studied, and not that of every other species out there.

Take these diagrams of baculum within different animal species for an example - Chipmunks/rats & Dogs & Orangutans - you can see that it is not the same for all species, so I would say that it is possible for their baculum to be retracted alongside their penises when not erect.