Osteology Everywhere: Vertebral Incidens

Try as I might, I can never escape osteology. Never. Just the other day, I was walking through my school’s expansive, boneless atrium, when these haphazardly scattered letters stopped me in my tracks:

2016-02-09 16.26.31

DЯSTUDENSN

Amidst this alphabet soup, there it was, calling out to me. Whispering. Longing….

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Ah, the dens. What is the “dens” you ask? It is a special little projection on a special little bone, the second cervical vertebra (C2). Why is it special? Well, most vertebrae look pretty similar to one another, with a body in the front being held in awkward embrace by a bony neural arch in the back.

 

But not the first two vertebrae, C1 and C2. No, these rebels are spinal celebrities. C1, whose rock name is “Atlas” (presumably in honor of its favorite episode of Wishbone) cradles the skull’s occipital condyles on its concave shoulders. Lacking a true body or centrum, Atlas viewed from the top resembles the gaping maw of a manta ray:

Top: Manta ray. Bottom: Atlas viewed from top, anterior is on the bottom (from Scheuer and Black, 200). A and F refer to the age at which the bony portions appear and fuse, respectively.

Top: Manta ray. Bottom: Atlas viewed from top, anterior is on the bottom (from Scheuer and Black, 2000). A and F refer to the age at which the bony portions appear and fuse, respectively.

Atlas is a jerk and so it sits right on top of C2, whose rock name is Axis (after the second album by the Jimi Hendrix Experience). More gawky and angsty than Atlas, Axis differs from the rest of the vertebrae in having an extension, the dens, which reaches skyward to boop the inside of Atlas’ maw:

Top: Axis viewed from the front. Bottom: Axis getting pwnd by Atlas. Modified from White et al. 2012.

Top: Axis viewed from the front. Bottom: Axis getting pwnd by Atlas. Modified from White et al. (2012).

The most distinctive feature of Axis, aside from its smoldering adolescent rage, is the dens (or odontoid process). If you find a bone fragment that is verily vertebral and has a perpendicular projection, you can bet good tenge you’ve got an Axis. Even a densless fragment can be distinguished from all other vertebrae by its superior articular facets, which are rather flat and face mostly superiorly.

What I thought would be a casual jaunt after class last week turned out to be a horrific reminder of the most amazing vertebrae. This must be  how Scott Williams always feels.

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One thought on “Osteology Everywhere: Vertebral Incidens

  1. Pingback: Worst year in review | Lawn Chair Anthropology

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