Bone Structure & Fisting
I was in the exam room at the chiropractor's office today waiting for her to arrive. She had a model of the spine in there very similar to this:
So, naturally, I couldn't resist slipping my hand through the pelvic opening.
Side-to-side, the opening was wide enough for my flat hand to go through easily. This, of course, is 90 degrees off of the anal sphincter, which is wider front-to-back. Her model did not have the pointy protrusions that this image has at 90 and 270 degrees. Perhaps the model in the office was from a female and the model in the image is from a male.
The major constriction I found on the model was between the front of the pelvic opening and the tip of the tailbone (coccyx). I was not able to get my balled fist through this opening.
I'm 6-foot-1 and the model was definitely shorter than me. I'd estimate it to be about 80 percent of my spinal column.
When the chiropractor came in, I asked her first whether the yellow tubes sticking out represented nerves. She said yes. Then I asked her if it was a full-scale model. She indicated it was but that it represented a person smaller than me. She said in taller people the spine (and by inference, the pelvis) would be proportionately larger.
I sure hope there's no security camera video of me slipping my hand through the pelvic opening of that model.
So 3 points:
(1) When going through the anal sphincter, the widest part of your hand or dildo should be aligned front-to-back.
(2) When going through the opening in the pelvic bone and coccyx, the widest part of your hand or dildo should be aligned side-to-side, or about 60 degrees off front-to-back if those point protrusions in this image is from a male.
(3) From my own experience with the Light House butt plug and research online, there is some flexibility in the coccyx and it is possible to coax the tailbone back away from the front of the pelvic opening. Based on my experience and other postings here, that will cause noticeable discomfort that might last 10 days to 2 weeks. In my experience, the increased flexibility appears to be permanent with periodic width play.
