Bird vertebra diagrams

January 10, 2014

bird neck note sheet

I made these back in the day. The idea was that you could print them out and have them along while dissecting bird necks, so you could draw on the muscles.

bird neck note sheet - LEFT - all three views

It’s basically one drawing of an ostrich vertebra, morphed in GIMP and stacked to simulate articulation. All of the ones in this post show the vertebrae in left lateral view. If you need right views, flip ‘em in GIMP or heck, I think even Windows Explorer will do that for you. The one above has dorsal views in the top row, lateral view in the middle row, and ventral views in the bottom row.

bird neck note sheet - LEFT - double lateral

Here’s a sheet with two rows in lateral view, the idea being that you draw on the more superficial multi-segment muscles on one row, and the deeper single- or two-segment muscles on the other row.

bird neck note sheet - LEFT - 12 cervicals

A version with 12 vertebrae, so you can map out the often complicated patterns of origins and insertions in the really long muscles. How complicated? Well, check out this rhea neck with the M. longus colli dorsalis and M. longus colli ventralis fanned out.

Rhea neck muscles fanned - full

That’s all. Have fun!

Vicki book arrival 3

When we last left my better half, Dr. Vicki Wedel, she was helping to identify a Jane Doe who had been dead for 37 years by counting growth rings in the woman’s teeth. That case nicely illustrated Vicki’s overriding interest: to advance forensic anthropology by developing new methods and refining existing ones. To that end, for the past few years she has been working with her PhD advisor, Dr. Alison Galloway at UC Santa Cruz, to revise and update Alison’s 1999 book, Broken Bones: Anthropological Analysis of Blunt Force Trauma. The revised and much expanded (504 pages vs 371) second edition, co-edited by Vicki and Alison, came out Monday (Amazon, Amazon.co.uk).

You can read the whole table of contents on Amazon (click to look INSIDE!), but the short short version is that the book has three major sections. The first covers the science and practice of trauma analysis (pp. 5-130), and the second classifies hundreds of common fractures throughout the skeleton, with illustrations (pp. 133-313). The chapters in these sections were all written by Vicki, Alison, and another of Alison’s former students, Dr. Lauren Zephro, solo and in varying combinations. Lauren, whom I always think of as “the Amazon cop”, is a 6-foot blackbelt forensic anthropologist for the Santa Cruz County Sheriff’s Office. If push came to shove I have no doubt that she could beat me to death with her bare hands and then produce a technical analysis of my corpse.

The final section (pp. 314-410) consists of nine case studies contributed by forensic anthropologists, pathologists, medical examiners, forensic and medical artists, and a DoD casualty analyst, based across the Anglophone world from Hawaii to Scotland. There’s some grim stuff in there: trauma to the homeless and elderly, from intimate partner violence, and from child abuse. It’s gut-churningly awful that the defenseless suffer from bone-breaking violence; it’s always been amazing to me that people like Vicki, Alison, Lauren, and the other contributors have both the courage to face these horrors and the technical chops to make the unspeakable solvable.

Beyond that unavoidable darkness, if you’re interested in the many, varied, and often just plain weird ways in which people die, the book is a treasure trove. There’s an elderly woman lying on her deathbed for six years, slowly turning into a natural mummy… (wait for it) …while her daughter went on living in the same house. There’s a classification of plane crashes with a description of what human remains will be found and over what area. There are people hit by trains; the funniest line in this very serious book is the deadpan and unsurprising, “The typical pedestrian hit by a train is male and often highly intoxicated.”

Fig 7-3 train skull

That’s from the top of page 122. At the bottom of the same page is my one contribution to the book, which also appears as the cover art (yeah, nepotism, whatcha gonna do). There’s a story behind this. This guy–yes, male, dunno if he was intoxicated–was hit by a train and his head was sheared in half, with the somewhat fractured but mostly intact facial skeleton separated by a lot of missing bone from the occipital region. With no way to obtain the deceased guy’s permission to use his mortal remains in the book, Alison and Vicki didn’t feel comfortable including their photos, so I spent a weekend bashing out a technical drawing for them to use instead. That reawakened my interest in pen-and-ink work and led to the dödö pöst.

I should say two things right here: first, that yes, I am hijacking the rest of the post to talk about myself. (Is anyone really surprised? I thought not.) Second, that I have had no training and possibly my stippling violates Art Rules or best practice guidelines of which I am ignorant. But I hope it also illustrates what can be achieved in a couple of days, with about $15 worth of supplies, by a guy whose only rule is “möre döts”.

So anyway, if you’re curious, here’s the method I use for my pen-and-ink illustrations:

  1. Get a decent-sized photo of the object to be drawn. I usually roll with $2 8x10s from MalWart, in this case one for each half of the skull.
  2. Tape the photo down to your work surface. I have a large, incredibly hard, perfectly smooth cutting board that I use for this, but in a pinch you could use just about anything, including just a larger piece of paper. Cardboard off the backs of desk calendars is nice.
  3. Over the photo, tape down a piece of tracing paper.
  4. Lightly trace the outline of the photo and all the major details in pencil.
  5. Once you’ve gone as far as you can with that, peel up one side of the tracing paper, unstick the photo from the work surface, and remove it. Stick the tracing paper back down the work surface.
  6. Using the uncovered photo as a reference, pencil in any other salient details by eye. Also contour lines for shadows. All of the pencil lines are going to be erased later, so don’t be shy.
  7. Whenever you decide you’re done with the pencil, get a good pen and start tracing, directly over the pencil lines. I tend not to be too persnicketty about my tools but decent pens are a real help here. For these recent works, I picked up a three-pack of beige-tubed Micron pens for $7 (this set).
  8. In all of the following pen-related steps, be careful to keep your big stupid hand and arm off the wet ink you just laid down–one careless smear can ruin a few hours’ work. Having a work surface that you can rotate is nice, so your pen hand can approach the drawing from any angle. Anytime I have to lay my hand on the drawing, I put down a piece of clean scrap paper first. Even if the underlying ink is dry, it just feels like a smart precaution.
  9. Once the lines are on, add döts to taste. With a little experimentation, you can get patterns of dots to not only indicate light and dark but also suggest textures. Different pen tips and amounts of pressure will yield dots of different sizes, which can also be useful. Dense, overlapping dots can produce an effect similar to scratchboard. BTW, sometimes I do “gear down” and place each dot with thought and care, but in the dense sections I just rat-a-tat-tat like a Lilliputian jackhammer. Try different speeds and see what you can tolerate.
  10. When you’re done dötting, at least to a first approximation, and you’re dead certain the ink is all dry, get a decent eraser and erase all of the pencil lines. I used one of those clicky mechanical erasers because it was cheap and soft enough to not tear up the paper.
  11. Re-ink any lines lightened by the erasing. I find that the döts are usually unaffected, but lines are often knocked down a bit by the eraser work. I suppose it would be cleaner to just draw natively in pen, with no prior pencilling and therefore no erasing, but the few times I’ve tried it, it hasn’t gone well. YMMV. If you’re drawing a 3D solid, this is a good time to employ an old illustrator’s trick, which is to make the bottom outline heavier and darker than the rest, to subtly convey a sense of weight.
  12. Scan, touch up as needed in GIMP, post to blog, bask in self-admiration.

In this case I had a few more steps, which consisted of making variants of the drawing and test-driving them by Vicki and Alison so they could pick their favorites.

Skull drawing - A

This is just embarrassing: after scanning the two drawings and doing a little touch-up, I just scooted them together until they looked like a skull. The problem is that the occiput is nowhere near anatomical position. See that flange of bone above the ear-hole, pointed down and right at a 45-degree angle? That’s the back end of the zygomatic arch, and it should be aimed at the forward stump of the arch, which is just down and back from the eye socket.

Skull drawing - B

Here’s the B version, where I was working entirely off of the zygomatic arch ends, and trying to get the skull into anatomical position. Scientifically this is probably the best variant I produced (I’m not claiming it’s the best possible), but aesthetically it’s a little crowded.

Skull drawing - F1 - original on white

I’ll spare you versions C-E, all of which just scooted the back end of the skull around in an attempt to find a balance between scientific and aesthetic concerns. Here’s the winning F version, which got used for the figure, and became the seed variant for the cover.

Skull drawing - F3 - yellow no fill

For the cover, we tried a lot of things, including the white skull on a black background, and one that was simply inverted from the figure. By this point the publisher had sent Vicki some test versions of the cover, and I thought it would be cool if the drawing was in the same color as the cover text, so I sampled that color from the publisher’s sample cover image and applied it to all of the drawn bits. They knocked it down a few tones for the printed version, so happily it’s not this garish.

Incidentally, I had never tried to replace a bunch of discontinuous areas of the same color with another color in GIMP, so I had to look it up. The two key steps are Select > By color, with the threshold set to zero (or not, if you want to grab a bunch of related colors at once), and “Fill whole selection” in the Bucket tool. Hat tip to this dude and his commenters.

Skull drawing - F5 - yellow 17pc fill

One last step: I thought the bare, unfilled yellow version looked too flat, so I tried different levels of fill to make the skull pop out from the background. I didn’t use bucket fill here–too fiddly with so many dots and edges. Instead I created a new layer of solid yellow and dropped the opacity to 17%. Then went to the drawing layer and used the magic wand tool to select the whole non-skull background. Then popped back to the yellow layer and cleared that selection, leaving yellow fill only in the boundaries of the skull outline. I also tried 10% and 25% opacity for the fill layer, but 10% was too subtle and 25% was starting to swamp some of the detail in the drawing. Between goofing around with colors and opacity levels we went through 10 versions at this stage, of which the one above is the ultimate champion.

So, that’s how the cover art came to be. Back to the book. There’s a bibliography with 1237 references (Vicki knows), and an index. The book is hardbound, with a printed cover and no dustjacket, and IMHO reasonably priced at $65, currently a few bucks less on Amazon. You probably already know whether you want a copy. If so, do the right thing–it’s not too late to get it by Christmas.

References

Wedel, V.L., and Galloway, A. 2013. Broken Bones: Anthropological Analysis of Blunt Force Trauma, Second Edition. Charles C. Thomas, Springfield, 504 pp.

Wedel, V.L., G. Found, and G.L. Nusse. 2013. A 37 year-old cold case identification using novel and collaborative methods. Journal of Forensic Identification 63(1): 5-21.

One aspect of sauropod neck cartilage that’s been overlooked — and this applies to all non-avian dinosaurs, not just sauropods — is the configuration of the cartilage in their necks. It’s not widely appreciated that birds’ necks differ from those of all other animals in this respect, and we don’t yet know whether sauropods resembled birds or mammals.

Here’s a classic sagittal view of a mammal neck — in this case a human — from The Basics of MRI (Joseph P. Hornak, 1996-2013):

sagittal-neck

You can see two distinct kinds of structure alternating along the neck: the big, square ones are vertebral centra (slightly hollow at each end), and the narrower lens-shaped ones are the intervertebral discs.

In mammals, and most animals, we find this distinct fibrocartilaginous element, the disc, between the centra of consecutive vertebrae. These discs have a complex structure of their own, consisting of an annulus fibrosus (fibrous ring), made of several layers of fibrocartilage, surrounding a nucleus pulposus (pulpy centre) with the consistency of jelly.

IntervertebralDisc

But in birds, uniquely among extant animals, there is no separate cartilaginous element. Instead, the articular surfaces of the bones are covered with layers of hyaline cartilage which articulate directly with one another, and are free to slide across each other. The adjacent articular surfaces are enclosed in synovial capsules similar to those that enclose the zygapophyseal joints. You can see this in the hemisected Rhea neck from last time:

Figure 18. Cartilage in the neck of a rhea. Joint between cervicals 11 (left) and 10 (right) of a rhea, sagittally bisected. Left half of neck in medial view. The thin layers of cartilage lining the C11 condyle and C10 cotyle are clearly visible.

Taylor and Wedel (2013c: Figure 18). Cartilage in the neck of a rhea. Joint between cervicals 11 (left) and 10 (right) of a rhea, sagittally bisected. Left half of neck in medial view. The thin layers of cartilage lining the C11 condyle and C10 cotyle are clearly visible.

The difference between these two constructions is very apparent in dissection: in birds, adjacent vertebrae come apart easily once the surrounding soft tissue is removed; but in mammals, it is very difficult to separate consecutive vertebrae, as they are firmly attached to the intervening intervertebral disc.

Figure 19. Alligator head and neck. Sagittally bisected head and neck of American alligator, with the nine cervical vertebrae indicated. Inset: schematic drawing of these nine vertebrae, from ([62]: figure 1), reversed.

Taylor and Wedel (2013c: Figure 19). Alligator head and neck. Sagittally bisected head and neck of American alligator, with the nine cervical vertebrae indicated. Inset: schematic drawing of these nine vertebrae, from ([62]: figure 1), reversed.

To complicate matters further, thin articular discs occur in the necks of some birds — for example, the ostrich (see illustration below), the swan, and the king penguin. But these discs do not occur in all birds — for example, they are absent in the turkey and the rhea. When they are present, these articular discs divide the synovial cavity and prevent the (cartilage-covered) bones on either side from ever articulating directly with each other, just like the articular discs in the human temporomandibular and sternoclavicular joints. These discs are thinner than the true intervertebral discs of mammals and crocodilians; and they are different in composition, lacking the annulus/nucleus structure and consisting of a simple sheet of fibrocartilage.

Taylor and Wedel (2013: Figure 4). Intervertebral articular discs of an ostrich (not to scale). Left: first sacral vertebra in anterior view, showing articular disc of joint with the last thoracic vertebra. Right: posterior view view of a cervical vertebra, with probe inserted behind posterior articular disc. The cervical vertebra is most relevant to the present study, but the the sacral vertebra is also included as it shows the morphology more clearly. These fibrocartilaginous articular discs divide the synovial cavity, like the articular discs in the human temporomandibular and sternoclavicular joints, and should not be confused with the true intervertebral discs of mammals and other animals, which consist of a nucleus pulposus and an annulus fibrosus.

Taylor and Wedel (2013: Figure 4). Intervertebral articular discs of an ostrich (not to scale). Left: first sacral vertebra in anterior view, showing articular disc of joint with the last thoracic vertebra. Right: posterior view view of a cervical vertebra, with probe inserted behind posterior articular disc. The cervical vertebra is most relevant to the present study, but the the sacral vertebra is also included as it shows the morphology more clearly. These fibrocartilaginous articular discs divide the synovial cavity, like the articular discs in the human temporomandibular and sternoclavicular joints, and should not be confused with the true intervertebral discs of mammals and other animals, which consist of a nucleus pulposus and an annulus fibrosus.

Crucially, the extant phylogenetic bracket (EPB) does not help us to establish the nature of the intervertebral articulations in sauropods, as the two extant groups most closely related to them have different articulations. As noted, birds have synovial joints; but crocodilians, like mammals, have fibrocartilaginous intervertebral discs. So their most recent common ancestor, the ur-archosaur, could equally have had either condition, and so could its various descendants.

vertebral-joint-type-cladogram

This seems like a mystery well worth solving. For one thing,  in the wholly inadequate database that we assembled for the paper, the birds had much thinner cartilage than the other animals. Since they are also the only animals with synovial neck joints, thin cartilage correlates with this kind of joint — at least across that tiny database. Is that correlation reliable? Does it hold out across a bigger sample? Is there a causation? If so, then finding out what kind of intervertebral joints sauropods had would help us to determine how thick their cartilage was, and so what their actual neutral posture was.

But we can’t tell this directly unless we find sensationally well preserved specimens that let us see the structure of the cartilage. We might speculate that since birds have unique saddle-shaped joints and sauropods have ball-and-socket joints like those of mammals and crocs, they’d be more likely to resemble the latter in this respect, too, but that’s rather hand-wavey.

Can we do better?

If we can, it will be through osteological correlates: that is, features of the bones (which are preserved in fossils) that are consistently correlated with features of the soft tissues (which are not). We’d want to find out from analysis of extant animals what correlates might exist, then go looking for them in the bones of extinct animals.

A couple of times now, I’ve pitched this as an abstract for a Masters project, hoping someone at Bristol will work on it with me as co-supervisor, but so far no-one’s bitten. Maybe next year. It would be a very specimen-based project, which I’d think would be a plus in most people’s eyes.

Figure 8. Cervical vertebra 7 from a turkey. Anterior view on the left; dorsal, left lateral and ventral views in the middle row; and posterior on the right.

Taylor and Wedel (2013: Figure 8). Cervical vertebra 7 from a turkey. Anterior view on the left; dorsal, left lateral and ventral views in the middle row; and posterior on the right.

Anyway, the awful truth is that at the moment we know spectacularly little about the cartilage in the necks of sauropods. We don’t know whether they had true intervertebral discs. If not, we don’t know whether they had articular discs like those of ostriches. We don’t know how thick these elements, if present, were. We don’t know how thick the hyaline cartilage on the bones’ articular surfaces was, or how evenly it covered its those surfaces.

And until we know those things, we don’t really know anything about neck posture or range of movement.

There’s lots of work to be done here!

Hemisected horse head

Continuing the recent theme. We’re not giving this a “Things to Make and Do” header because the spirit of that category is to showcase anatomical preparations that average people could do in the comfort of their own homes and gardens (provided they can get hold of dead wallabies, bear skulls, etc.), and freezing and band-sawing a horse is probably outside that envelope for almost everyone (I hadn’t though of that when I posted the gator!).

In the spirit of MYDHHH:

Hemisected horse head with scale

This ain’t mine, it’s a teaching specimen from our vet school, which has a no-kill policy. All of the animal cadavers used in the anatomy labs are donated by the owners at the ends of the animals’ natural lives. So no animals were harmed in the making of this science.

But I wish it was mine. And as long as I’m dreaming, I’d like a pony. Anyone want to go halvesies?

Hemisected gator

Okay, before some wag makes this point, the gator is missing a good chunk of its tail, so this is more like the left half of the anterior two-thirds of a gator. But that would make a lousy title.

We might have more to say about this in the future, but for now, I’m going to let this 1000-word-equivalent speak for itself.

Many thanks to Elizabeth Rega for the use of the gator.

Another picture from the recent ostrich dissection (click for full-size, unlabeled version). Last time we were in the middle of the neck, looking from anterior to posterior. This shot is from closer to the base of the neck, looking from posterior to anterior. A lot of the stuff is the same: the ragged cut from the saw at the meat processing plant where the ostrich was cut up; the spinal cord with the supramedullary airways above it in the neural canal; and the large interspinous ligament with diverticula on either side. We’ll have reason to refer back to some of those things in the not-too-distant future, but right now I want to draw your attention to something else: the tendons of the paired longus colli dorsalis muscles toward the top of the photo.

Here’s a modified version of Wedel and Sander (2002: fig. 2) with the course of the longus colli dorsalis highlighted in red (anterior is to the left). It is a curious aspect of bird necks that the large dorsal muscles do not insert on the neural spines but on the epipophyses (or dorsal tori or dorsal tubercles) above the postzygs. A naive approach based on beam theory would suggest that inserting on the neural spines would give those muscles more leverage, but necks are tricky and often defy such a priori predictions.

Instead of inserting on the neural spines, the longus colli dorsalis muscles originate from them, especially in the posterior part of the neck, and that’s what the photo at the top shows. From the reader’s point of view, the big interspinous ligament runs forward to attach to the posterior side of the neural spine (not visible because it’s buried in gloop, but it’s about a third of the way down from the top). The longus colli dorsalis tendons are running forward from the anterior side of the neural spine.

Fig. 20. An MRI of the mid-cervical series of an ostrich (Struthio camelus). In sagittal section, the interspinous ligaments are lighter than the surrounding muscle because of their high fat content. The neural canal is occupied by the spinal cord and supramedullary pneumatic airways. Also apparent in this image are the tendons of the longus colli dorsalis muscle originating from the neural spine. Scale bar is 4 cm.

Here’s the same thing again, also in an ostrich, but in an MRI this time (and with anterior to the right; Wedel et al. 2000: fig. 20). The dark streaks running forward from the neural spines are those longus colli dorsalis tendons. The interspinous ligament also shows up nicely as a series of white bands connecting adjacent neural spines.

References

Those ostrich necks I went to Oro Grande to get last Thursday? Vanessa and I started dissecting them last Friday. The necks came to us pre-cut into segments with two to three vertebrae per segment. The transverse cuts were made without regard for joints so we got a bunch of cross sections at varying points through the vertebrae. This was fortuitous; we got to see a bunch of cool stuff at the cut faces, and those cut faces gave us convenient avenues for picking up structures and dissecting them out further.

In particular, the pneumatic diverticula in the neck of this ostrich were really prominent and not hard at all to see and to follow. The photo above shows most of the external diverticula; click through for the full-resolution, unlabeled version. The only ones that aren’t shown or labeled are the diverticula around the esophagus and trachea (which had already been stripped off the neck segments, so those diverticula were simply gone), those around carotid arteries, which are probably buried in the gloop toward the bottom of the photo, and the intermuscular diverticula, of which we found a few in parting out the dorsal and lateral neck muscles.

There is one final group of diverticula that are shown in the photo but not labeled: the interosseous diverticula that fill the air spaces inside the bone.

We have tons of cool photos from this dissection, so expect more posts on this stuff in the future.

For previous posts showing diverticula in bird neck dissections, see:

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

Things to Make and Do, part 7b: more fun with rhea necks (admittedly, not the most creative title ever)

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