The equine interspinal ligaments of Ray Wilhite

March 13, 2023

Our old friend Ray Wilhite sent us this glorious photo of a horse neck that he dissected recently, with permission to post here:

The big yellow sheet at the top is the nuchal ligament, which in many mammals provides axial tension for the cervical vertebrae, and which has been hypothesized (e.g. by Alexander 1985:13) to have existed and provided similar support in at least some sauropods.

But what caught Ray’s eye was the smaller interspinal ligaments running horizontally between the neural spines of the consecutive vertebrae. The literature doesn’t talk about these much because the irresistible glamour of the nuchal ligament grabs everyone’s attention, but they’re there in pretty much everything, being primitive for tetrapods.

Here they are again in absolutely glorious detail. (Seriously, click through for the full-sized version. You can all but make out individual cells.)

Many thanks to Ray for sharing these photos with us!

8 Responses to “The equine interspinal ligaments of Ray Wilhite”

  1. Ben Says:

    Fascinating. Was something removed from the pre/postzyg articulation, or do they really just float in space like that?

  2. Matt Wedel Says:

    I can see the prezyg-postzyg joints, so I assume that the fibrous joint capsules around those articulations have been removed. There’s still a lot of white connective tissue adhering to the bone where the joint capsules attached. I’ll post a labeled version showing what I’m seeing if I get time today.

  3. Ben Says:

    pictures like this are amazing. It never ceases to surprise me how little info there is (there seems to be?) on anatomical features that dinosaur workers study. A Google images search for postcranial pneumatization yields lots of colored dino diagrams, but nothing like the above showing what actual postcranial pneumatization looks like. Not sure if its hard to get at and photograph, but it can’t be harder than inferring it from really old bones. Maybe just part of an overall trend where some things somehow become uninteresting in extant species. In any case, not a mistake this blog makes.

  4. Mike Taylor Says:

    You are certainly right, Ben, that the extant-animal literature has often proven to have really surprising gaps in areas that we have just assumed would be well documented. (Or perhaps it’s that we’re not good at searching the extant-animal literature.)

    Note, though, that the images in this post don’t show postcranial pneumatization — which is unknown in mammals except in pathological cases — but cervical expaxial ligaments.

  5. Ben Says:

    Didn’t mean to suggest this horse had pneumaticised its neck–the image just reminded me how rare it is to find pics of extant things that are interesting in extinct things. Now, a horse smart enough to pneumaticise his neck would be interesting, and make all the the giraffes jealous.

  6. “Note, though, that the images in this post don’t show postcranial pneumatization — which is unknown in mammals except in pathological cases —”

    Didn’t the giant rhino Paraceratherium have hollowed out vertebrae as well?

  7. llewelly Says:

    wait, what, post-cranial pneumaticity in Paraceratherium ??? Are you sure? Can you find a link?

  8. Matt Wedel Says:

    Didn’t the giant rhino Paraceratherium have hollowed out vertebrae as well?

    Hollowed out, yes. Pneumatic, probably not. The transverse foramina for the vertebral arteries are ballooned out until they occupy essentially the entire centrum, BUT as far as I know the passages are smooth and don’t have any of the sculpturing, fossae, or chambers that are diagnostic for pneumaticity. To me that suggests that the empty spaces were occupied by fat and blood vessels, and not by pneumatic diverticula. I know I’ve seen cross-sections of those vertebrae, possibly in one of Janensch’s papers. If I find the right image, I’ll post it.

    UPDATE a few minutes later: the Paraceratherium vert is illustrated and discussed by Janensch (1947), following the description by Forster Cooper (1923). I have both papers, including a translation of Janensch (1947), and I’ll get a post up on this stuff soon — hopefully this weekend.

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