Things to Make and Do, part 7b: more fun with rhea necks

August 23, 2011

Wedel’s Theorem:

freezer full of interesting dead animals + great anatomy student who actually wants to get up on Saturday morning and dissect = happiness

The rhea has been the gift that keeps on giving. Saturday was my fourth session with some part of this bird, going back to 2006 (previous posts are here, here, and here). The first two sessions were just about reducing the bird to its component parts, and the last session was all about midline structures.

The goal for the neck is to dissect down to the vertebrae and document everything along the way–muscles, tendons, fascia, blood vessels, and especially diverticula. In the past I have been pessimistic about the chances of seeing diverticula without having them injected with latex or resin or something. But this bird is changing my mind, as we saw in a previous post and as you can see below.

The goal for Vanessa is to grok all of this anatomy, and hopefully make some publishable observations along the way. She has a chance to do something that I think is rather rare for a sauropod paleobiologist, which is to get a firm, dissection-based grounding in bird and croc anatomy before she first sets foot in a museum collection to play with sauropod bones.

That sounds awesome, and probably will be awesome, but before there can be any awesomeness, the fascia has to be picked off the neck. And by ‘picked’ I mean ‘actually cut away, millimeter by arduous millimeter’. It wasn’t that bad everywhere–the fascia over the long dorsal muscles came off very easily. But the lateral neck muscles were actually originating, in part, from the inner surface of the fascia. That’s not unheard of, it happens in the human forearm and leg all the time, but I’ve never seen it as consistently as in this rhea. So picking fascia took a loooong time–that’s what Vanessa is doing in the photo at top.

Once the fascia was off, Vanessa started parting out the long tendons of the hypaxial muscles in the left half of the neck. Meanwhile, I started stripping fascia from the right half. I had forgotten that the right half of the neck still had the trachea and esophagus adhered to the side. That probably sounds weird, given that our trachea and esophagus–and those of most mammals–run right down the middle of our necks and aren’t free to move around much. In birds, they’re more free-floating and can drift around between the skin and the vertebral muscles, sometimes even ending up dorsal to the  vertebral column–there’s a great x-ray of a duck in a  2001 paper that shows this, which I’ll have to blog sometime.

Anyway, when I cut the fascia to pull back the trachea and esophagus, I found that they were separated from the underlying tissues by a dense network of pneumatic diverticula winding through the fascia.

I had heard, anecdotally, of networks of diverticula described as looking like bubble wrap. I can now confirm that is true, for at least some networks. What was especially cool about these is that they were occupying space that would be filled with adipose or other loose connective tissue in a mammal, which illustrates the point that pneumatic epithelium seems to replace many kinds of connective tissue, not just bone–something Pat O’Connor has talked about, and which I also briefly discussed in this post.

I should mention that there was no connection between these diverticula and the trachea, as there is between the subcutaneous throat sac and the trachea in the emu (story and pictures here).

While I was geeking out on diverticula, Vanessa was methodically separating the long hypaxial muscles, which looked pretty cool all fanned out.

And that’s all we had time for on Saturday. But we’re cutting again soon, so more pictures should be along shortly.

13 Responses to “Things to Make and Do, part 7b: more fun with rhea necks”

  1. Mike Taylor Says:

    Extremely awesome bubble-wrap photo.

    You asserted that “there was no connection between these diverticula and the trachea, as there is between the subcutaneous throat sac and the trachea in the emu”. How sure are you that there is no connection at all? Or are you only making the weaker claim that if there is a connection somewhere along the length, then it’s much smaller than in the case of the emu throat-sac and you’ve not found it yet?

  2. Matt Wedel Says:

    I’m dead sure–once I had the trachea all the way off, I checked for holes, and there weren’t any. My guess is that these paratracheal diverticula are branches off the clavicular air sac, which sends all kinds of funky diverticula around the shoulder joint and among the thoracic viscera. But the rest of the bird is long gone so I have no ready way to test that guess. Maybe some luckier person with a complete dead rhea will leap into the gap.

  3. Mike Taylor Says:

    I suppose the thing to do would be close off one end of the trachea, then try to inflate it by blowing in the other end. That would establish the absence of even tiny perforations.

  4. Dave Godfrey Says:

    Something that occurs to me after reading the X-men origins post is that pneumatic epithelium acting as packing material (instead of fat as in mammals and other reptiles) might be cheaper to grow than fat. Not sure how you’d test this however.

  5. Matt Wedel Says:

    Yeah, that’s a darn good point. Cheaper to grow, cheaper to maintain, cheaper to move…just cheaper all around. As you point out, though, testing is the sticking point. We know very little about the physiological behavior of these diverticula. If we’re going to sort out how and why they evolved, we need to know more.

  6. […] a recent post I showed photos of the trachea in a rhea, running not along the ventral surface of the neck but […]

  7. Intrested in animals anatomy Says:

    is studying anatomy difficult, and how much it take , and what are the majors in studying anatomy for animals to be specific ?
    where i should go to start ?

  8. Matt Wedel Says:

    is studying anatomy difficult, and how much it take

    I suppose it depends on whether you’re approaching anatomy with an eye toward getting a job in the field, or for its inherent interest but without any designs on employment.

    If for a job, you’ll probably need a postgraduate degree, either an MS or PhD, in a relevant field, about which more in a second.

    If for personal interest, all you need is a source of dead animals and some curiosity. Mike’s posts in this series should give you some ideas; he’s essentially self-taught as an anatomist (aren’t we all, though?–at the end of the day, you really learn anatomy with something dead in front of you and scalpel in hand) and he’s been quite successful at acquiring interesting animals to dissect.

    and what are the majors in studying anatomy for animals to be specific?

    Oh, loads. Anthropology, veterinary medicine, organismal biology, paleontology…the list goes on. There is no one clearly defined path to anatomy. Even as professionals it is something that some of us are more into than others. It almost seems that people who want to be anatomists find a way to make it happen, regardless of what degree program they are in or whether they are in academia at all. Taxidermists, for example, usually know a ton of anatomy from working with dead animals.

    where i should go to start?

    Get something dead and cut it up. A roadmap to what you’re cutting is often useful; you may be able to find some anatomical reference books at your local public library or through Amazon. This book is the finest general vertebrate dissection guide I have ever seen: the illustrations are just gorgeous and it is one of the few that pays more than lip service to vertebrate phylogeny. Whatever animal you’re cutting up will probably be sufficiently close to one of the model organisms in the book for it to be useful (an ostrich isn’t _that_ different from a pigeon, etc.).

    If you need more technical resources (i.e., scientific papers), I am happy to report that acquiring them is a solved problem: here are your instructions.

    Hope all this helps! Good luck with your quest, it’s a noble one.

  9. […] rhea was dissected by Vanessa back at Western a couple of weeks ago, the turkey by me on Mike’s dining room table on […]

  10. Jack Says:

    In emu, the tracheal diverticulum is present. In the lower part of the trachea, just before the thoracic inlet, is a segment of trachea comprised of 7 to 12 incomplete rings that form a tracheal diverticulum or open cleft. A very thin membrane covers this cleft. During breeding season this membrane inlarges, creatng a pendulous pouch. This pouch is easy to see in females during their first three years of breeding, but in subsequent years does not enlarge as much. Males also have this cleft, but the membrane does not enlarge as much. This cleft is the source of the booming and grunting.

  11. Matt Wedel Says:

    Yes, that’s why in the post I said,

    I should mention that there was no connection between these diverticula and the trachea, as there is between the subcutaneous throat sac and the trachea in the emu (story and pictures here).

  12. […] Things to Make and Do, part 7b: more fun with rhea necks (admittedly, not the most creative title ever) Share this:FacebookRedditTwitterLike this:LikeBe the first to like this post. Posted by Matt Wedel Filed in dissection, DIY, ostrich, pneumaticity, stinkin' theropods, Uncategorized Leave a Comment » […]

  13. […] These long cervical ribs are ossified tendons of ventral neck muscles, presumably longus colli ventralis. We know they’re ossified tendons because of their bone histology (Klein et al. 2012), and we suspect that they’re longus colli ventralis because those tendons look the same in birds, just less ossified, as in this rhea (same specimens as these even older posts: 1, 2): […]

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