Things to Make and Do, part 31: redneck CT-scan

March 3, 2022

For reasons that would be otiose, at this moment, to rehearse, I recently found myself in need of a hemisected turkey cervical. Happily, I own five skeletonised turkey necks, so it was with me the work of a moment to select a candidate. But now what? How to hemisect it? We have  discussed plenty of hemisected things here at SV-POW!, but they tend to have been produced using heavy machinery such as a band saw: something that I singularly lack.

SPOILER: I found a way. Here is a domestic turkey Meleagris gallopavo domesticus, 9th cervical vertebra, hemisected, in right medial view. Read on to discover the extremely high-tech approach that yielded this prize. It’s propped up on some kind of turkey bone to help me get a good medial perspective, I am thinking maybe the pygostyle?

One idea was to use an angle-grinder: not to cut down the midline of the vertebra — it would be much too blunt and powerful for a small, delicate vertebra — but to use as a sanding surface, locking the grinder in place and holding the vertebra up against the spinning plate. That might work well, assuming I could find a way to secure the angle grinder safely, but as it happened my need for a hemisected vertebra came up during a power cut. (Thanks, Storm Eunice!)

So I did it the way the Amish do their vertebral hemisections: by hand, simply by rubbing the vertebra against a sheet of sandpaper:

CT scanning: the Amish method.

This is not as laborious as you might think. I used a single sheet of medium-grade sandpaper, and it took maybe 15–20 minutes. And I just rubbed back and forth while exerting downward pressure. Initially I worked my way only through the prezygapophyseal ramus, which is the part of the turkey cervical that extends the furthest laterally. Once I was satisfied that the plane between eroded prezyg and the intact postzyg was parasagittal, I just kept the vertebra parallel to the sandpaper and kept rubbing. (Sorry I didn’t think to get a photo at this stage.)

One thing that took me by surprise is that there was so very much bone dust. I mean, I am an idiot that this surprised me, since the whole purpose of this exercise was to reduce one half of this vertebra to bone dust. But the lesson to be learned here is to do it on the easily-cleaned bathroom floor — not on the desk next to the computer keyboard and above a carpet. Learn from my mistakes, folks!

Anyway, after some work on the prezyg/postzyg pair, here’s how the vertebra was looking:

You can see straight away that the prezyg ramus, postzyg ramus and parapophyseal ramus are extensively pneumatized, honeycombed with small, irregular air-spaces. In this image it looks like the region of bone between the pre- and postzygs is much more solid, but this is an illusion: what we’re seeing here is a section through the cortical  bone of the neural arch, cut parallel to the surface. Let this be a warning not to over-interpret individual slices of CT-scans!

Once we get a little deeper, we see that the whole wall of the neural arch — and indeed the centrum and the neural spine — is honeycombed, just like the zyg rami:

Now we have another area of what I’m going to call Phantom Apneumaticity: the posterior part of the centrum looks like solid bone, apart from a few pneumatic spaces in the posteroventral extremity. Again, this is an illusion.

Here’s the next place I stopped:

Here, the Phantom Apneumaticity is even more striking: seeing just this as a CT slice could easily mislead someone into thinking that almost the whole of the posteroventral part of the centrum is solid bone. But again, it’s just that we’re very close to the surface of the bone, and seeing a slice parallel to that surface.

This last image also shows an important point of technique: there is a low convex ridge running across the phantom apneumatic area from the top of the cotyle to the base of the centrum. This is where I had changed the angle I was holding the vertebra at, so I accidentally sanded the posteroventral part of the vertebra more than the rest. I found that it was important during this process to keep checking the angles, and to adjust: making sure I wasn’t sanding more from the front than the back, or from the top than the bottom, or leaving a ridge like this.

Also in this last photo you can see that I was just beginning to break through into the neural canal: the anterior part of it is now exposed, between the anterior part of the neural spine and the anterior articular surface. At this stage I sighted along from in front to get a sense of how much further I had to go:

Domestic turkey Meleagris gallopavo domesticus, 9th cervical vertebra, most of right side removed, in anterior view with dorsal to the right. Propped up on the coracoid of a different, larger, turkey.

Quite a way, I guess. Here it is rotated and cropped, so you can more easily recognise it:

Domestic turkey Meleagris gallopavo domesticus, 9th cervical vertebra, most of right side removed, in anterior view. You can see that the neural canal is still mostly intact.

More sanding was required. I sanded some more.

You’ve already seen the final result up at the top of the page, but here is a cleaned-up version of that image, oriented according to Definition 3 of Taylor and Wedel (2019):

Domestic turkey Meleagris gallopavo domesticus, 9th cervical vertebra, hemisected, in right medial view.

And if that isn’t beautiful, what is?

The exciting thing is, anyone can make one of these. Matt’s already explained how to extract and clean up bird vertebrae and given you some ideas of what to do with them. Prepare out some turkey vertebrae and get going with the sandpaper!

I leave you with one more image: the hemisected vertebra in anterior view, oriented with dorsal to the top, and mirrored so it make up a complete vertebra once more. Enjoy!

References

 

11 Responses to “Things to Make and Do, part 31: redneck CT-scan”

  1. Nick G Says:

    mike,

    the next logical extension for a make and do on this would be to take another cervical vertebrae and repeat this but with imaging each plane as you sand it off. Check it out:
    https://bmccancer.biomedcentral.com/articles/10.1186/s12885-021-08542-9

    https://link.springer.com/article/10.1007/s00345-018-2202-1

    https://www.jpathinformatics.org/article.asp?issn=2153-3539;year=2015;volume=6;issue=1;spage=6;epage=6;aulast=magee

  2. Mike Taylor Says:

    Exactly, Nick — that was what I was referring to (admittedly rather obliquely) by calling this a redneck CT-scan. With enough patience you really could do it in (say) 0.5 mm slices, then stack them in a computer and make them into a 3d model of the interior of the vertebra.

  3. Matt Wedel Says:

    That’s basically what Yara Haridy did to the jawless fish bones with FIB-SEM (this post). Would be kinda cool to do a low-tech version with a turkey vert, sandpaper, and a digital camera.


  4. Have you been reading Wodehouse lately? In any case a very cool project, and a reminder that low-tech solutions don’t stop working just because high-tech ones become available. A suggestion for future sanding projects: get some wet-dry sandpaper, adhere it to a
    flat surface (glass or tile are ideal) with spray adhesive, and use water while sanding. This cuts down on drifting dust, and you can rinse dust away when the sandpaper becomes clogged.

  5. Mike Taylor Says:

    Nathan:

    “Have you been reading Wodehouse lately?”

    Yes! I’m delighted someone spotted it! Wodehouse is responsible for “it was with me the work of a moment to …”, but did you spot the other (somewhat more recent) literary allusion?

    “Low-tech solutions don’t stop working just because high-tech ones become available.”

    That is very well put!


  6. The “otiose” line tickled my memory, but I can’t come up with the culprit. Or was that not the other quote?

    As it happens, I just watched a series of YouTube videos by sheet metal fabricator Ron Covell about turning an angle grinder into a stationary sander. The videos are titled “Dedicated Disc Maker” parts 1-3. His device is more complicated than what you would need for hemisections but might be a good source for ideas if you choose to go down that route in future.

  7. Mike Taylor Says:

    Yes indeed, Nathan:

    ‘You are speaking with Svlad, commonly known as “Dirk” Cjelli, currently trading under the name of Gently for reasons which it would be otiose, at this moment, to rehearse. I bid you good evening. If you wish to know more I will be at the Pizza Express in Upper Street in ten minutes. Bring some money.’

    ‘Dirk?’ exclaimed Richard. ‘You… Are you trying to blackmail me?’

    ‘No, you fool, for the pizzas.’ There was a click and Dirk Gently rang off.

    From Douglas Adams’ Dirk Gently’s Holistic Detective Agency, of course.

  8. llewelly Says:

    now I feel rather obtuse, bc I assumed “otiose” was just part of Mike’s normal vocabulary, rather than part of a reference to the Douglas Adams novel I have probably reread more than any other Douglas Adams novel.

  9. Mr. S... Says:

    Apologies if this seems insulting by asking you but,…

    How well do you know the skeletal anatomy of an emu skull? I’m piecing together a skull and have some mystery bones left over that I don’t know where they fit.

  10. Mike Taylor Says:

    Hi, Mr. S. I’ve never owned or even seen an emu skull; but I have played extensively with an ostrich skull, reducing it to its individual elements and reassembling it. The big image at the top of Things to Make and Do, part 6d: Veronica the ostrich skull, laid bare is probably going to be most useful, but do check the whole series that that post is part of. Good luck!

  11. Nathan Myers Says:

    I picture the vert encased in plaster, secured to a sort of pantograph to keep its orientation constant as it moves about. In place of photographic images, you could periodically press it to an inkpad and stamp a few images.

    That is how I imagine a Victorian gentleman-naturalist going about this. I have a suspicion that for (“true”) authenticity, gutta-percha would need to be involved somewhere.


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