Tutorial 2: Basic vertebral anatomy

October 4, 2007

At the risk of turning this blog into Brachiosaurus brancai 8th Cervical Picture of the Day, here’s a quick tutorial on your basic sauropod vertebral anatomy, using everyone’s favourite cervical vertebra.

Brachiosaurus brancai, 8th cervical, various views

This picture shows the same vertebra as was photographed in the very first SV-POW! entry.  I’ve composited the figures of this element from Janensch (1950), an exhaustive and lavishly illustrated monograph on the vertebrae and ribs of B. brancai. Parts of this vertebra’s right-hand side are missing, as is apparent in the anterior and posterior views, but most of it is excellently preserved.

First things first: directions. In standard anatomical descriptions of dinosaurs, the direction towards the front is called anterior, and towards the back is posterior — so an anterior view (such as the top left part of this picture) is looking at the front of the vertebra. Upwards is dorsal, downwards is ventral. Sticking out sideways is lateral, and towards the midline is medial. These directions can be combined into single words that describe oblique directions such as anteroventral, posterolateral and anteroventromedial. (Some poor misguided souls use “cranial” and “caudal” in place of “anterior” and “posterior”, but we’ll have none of that here.)

The main body of the vertebra, the roughly cylindrical part, is called the centrum. At the front of the centrum in sauropod cervicals and most dorsals is a ball which fits into a corresponding socket at the back of the preceding one. The ball is called a condyle, the socket is called a cotyle.

Dorsal to the centrum is the neural arch, which is surmounted by the neural spine. A hollow passageway runs through the neural arch from front to back: this houses the spinal cord, and is called the neural canal. (You can’t really see it in the pictures above; you can make it out much more clearly in the BMNH R2523 photos, anterior and posterior.)

Two processes (which just means pointy bits) project laterally from each side of the vertebra: in cervicals they mostly hang downwards a bit, i.e. they project ventrolaterally. (It is a bit of a mystery to me why we say “project ventrolaterally” in scientific writing instead of “hang down”, but there it is.) The dorsal pair of processes are the diapophyses (singular diapophysis, pronounced dye-a-POFF-a-siss). The ventral pair are the parapophyses. They are the articulation points for the ribs. In cervical vertebrae, the ribs are often fused to the processes that support them; in dorsal vertebrae they are free, attached only by soft tissue. (In the pictured specimen, the ribs are broken off very close to their point of origin. In life, they would have projected backwards as thin cylinders a couple of meters long.)

As you see, the diapophysis, parapophysis and fused cervical rib form a loop lateral to the centrum. This loop doesn’t really have a name — it’s called the ansa costro-transversaria in birds, but very few palaeontologists use avian anatomical nomenclature for sauropods. So we three just call it the “cervical rib loop”.

Finally (for now), we have the zygapophyses. There are two pairs of these: prezygapophyses at the front, and postzygapophyses at a location that I will not insult your intelligence by stating. When vertebrae are strung together in a line, their zygs articulate, but they can slide past each other to a limited degree, allowing some flexibility. How much flexibility is a matter of some debate which we may revisit in another post.  The facets of the prezygs always face anteromedially (that’s upwards and inwards, remember?) and the postzygs ventrolaterally, although their precise orientation varies along the spinal column.

That it for now. Coming soon in subsequent tutorials: fossae and foramina; laminae; variation along the column; and much, much more. Remember to tell all your friends that this is where the party is.

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23 Responses to “Tutorial 2: Basic vertebral anatomy”

  1. Mike from Ottawa Says:

    Thanks for the pronunciation tip on diapophysis. Being able to pronounce things helps a lot to cement them in the mind. To that end, is the first “y” in zygapophysis long or short? In my job in government contracting policy, zygapophysis doesn’t come up in conversation, though once I know how to pronounce it, I’ll find a way to work it in. ‘How’re you doing, Mike?’ ‘OK, I guess but one of my zygapophyseal joints is acting up on me’ ‘Must be this damp humid weather eh.’

    Oh, and you were worried about insulting our intelligence. After this post, I’m sure we’ll hear no more of that! :-)

  2. Emile Says:

    Dye-a-POFF-a-siss? Not dye-a-pof-I-siss? Dang! I’ve had it wrong all along… How does one pronounce zygapophysis then?

    Avian anatomical terms do not seem to work with sauropods, for some reason.

  3. Mike Taylor Says:

    Emile,

    I think most scientific terms — anatomical and taxonomic — are open to a certain amount of leeway in how they’re pronounced. You can go to a conference and hear the name Diplodocidae pronounced anywhere between Dip-loh-DOCK-i-day and Dip-loh-duh-SIDE-ee. Often there is no definitively correct pronunciation. That said, I’ve heard POFF-a-siss much more often than pof-I-siss, and that applied for dia, para- and zyga- versions.

    When Jerry Harris named the sauropod Suuwassea (Harris and Dodson 2004) he did the world a big favour by explicitly stating in the paper how that name is intended to be pronounced (SOO-oo-WAH-see-uh). But I’ve heard even that name mispronounced. It’s not the end of the world, is all I’m saying.

  4. Mike from Ottawa Says:

    Never mind the -pophyses (wasn’t that a punk album title?), is the y in zyg pronounced like the i in “zigzag” or like the y in xylophone?

  5. Mike from Ottawa Says:

    Merci beaucoup!

  6. Emile Says:

    Got it. Thanks!


  7. […] articular surface, while the concave cotyle is located on the anterior articular surface (see Turotial 2 if you need help with these terms). Vertebrae that have their concave articular faces positioned […]

  8. David Marjanović Says:

    Avian anatomical terms do not seem to work with sauropods, for some reason.

    They do work most of the time. They are mentioned here because they are standardised and much more easily applicable than the human terms, which are also standardised.

    The one in question should be “ansa costotransversalis”, though, if I’ve correctly guessed that “ansa” is singular.

  9. Mike Taylor Says:

    I am not going to get into Jerry Harris Wars here, but maybe some time in the future we’ll do a post on why, for such a smart person, Jerry did such a dumb thing when he renamed all the laminae :-)

  10. maria perez Says:

    Pleeease, give me an idea about the size of this vert!!!I am working with vertebrae very similar to the wealden bmnh 90, and wondering how they compare, size-wise.
    thanks, maria

  11. Mike Taylor Says:

    Hi, Maria, nice to hear from you. According to Janensch (1950: 44), this vertebra is 113 cm long from the prezygapophyses to the posterior margin of the centrum. The long prezygs significantly overhang the centrum in Brachiosaurus, though, so the length of the centrum alone is “only” 98 cm. Then again, the “functional length” of the vertebra — the length with which it acts within the whole physical system of the neck — is the length of the centrum minus the condyle, which in life would of course have been buried within the cotyle of the next vertebra. That functional length is 86 cm.

    By the way, it’s absolutely typical of Janensch that his table gives all three of these lengths. His work is characterised by a rigour and comprehensiveness that I’ve rarely seen elsewhere. Great papers. If only they weren’t written in German …

    It is very interesting that you’re working on vertebrae similar to BMNH R90! Where is your material from, and who are you working with? If you’d like to send us a photo or two, we’ll be happy to post them here. (Plus I’d like to see them for my own curiosity, of course.)

  12. Darren Naish Says:

    Mike – I think Maria’s question about size concerns R90, not the Brachiosaurus cervical vert pictured here. But I could be wrong.

  13. Mike Taylor Says:

    Possible. I’ve not measured R90a, but I remember it as being something like 40 cm tall.


  14. […] vertebrawesome. And a nice job it is. Still, I feel funny about you not getting a new picture (ahem), so I’m posting my late entry anyway. For some reason, despite–or perhaps because […]


  15. […] need help with some of the following anatomical terms do remember you’ve got our excellent tutorial on vertebral anatomy to help you]. The picture shown here (it’s Fig. 5 from Taylor & Naish 2007) shows […]


  16. […] you’ll recall from an earlier post, the neural canal is the hole in a vertebra through which the spinal cord passes. As you can see […]


  17. […] version, just in case the verbal description made no sense. I know Mike covered this stuff back in Tutorial 2, but Apatosaurus is frankly pretty freaky in the cervical rib […]


  18. […] sweeping out laterally from the sides of the vertebrae (if you need help with those terms go to Tutorial 2). This mount is nice in showing how wide the neck base was in broad-necked taxa like Camarasaurus […]


  19. […] of motion.  (”neutral pose” here means that the vertebra are aligned such that the zygapophyses overlap as much as possible.) Diplodocus carnegii, DinoMorph computer model , showing neutral neck […]


  20. […] from paired ossification centers on either side of the cartilaginous notochord (see Tutorials 1 and 2 if you need to brush up on vertebral anatomy). The neural arches also start out as left-and-right […]


  21. […] Back in the early tutorials, we covered skeletal details such as regions of the vertebral column, basic vertebral anatomy, pneumaticity and laminae, but we never started out with an overview of the sauropod […]


  22. […] Berlin. We spent some time down in the collections, where we were particularly pleased to see the much-admir’d C8 of Giraffatitan‘s paralectotype, MB.R.2181 (previously known as HMN […]


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