OsteoMenagerie 3: The petrous portion of the temporal bone

The petrous portion of the temporal bone provides passage for the facial (VII) and vestibulocochlear (VIII) nerves, houses some of the body’s most delicate organs of hearing (including the auditory ossicles) and is one of the densest bones in the body. As such it tends to be one of the better preserved cranial bones. You’re likely to come across it even at  sites where most cranial bones are highly fragmented or commingled, and you’ll definitely come across it on bone quizzes if your instructor has any sort of penchant for archaeology. It’s  important to be able to side it, particularly when isolated, as taphonomy is normally far kinder to the petrous portion of the temporal than it is to the squamous or mastoid portion. Personally, when I look at the petrous portion in posterior view, I see a dragon. Maybe it’s all the recent uproar about GoT (if you have no idea what I’m talking about, watch this trailer, it’ll get you piloerect in no time), but I think there’s something to the visual metaphor. To wit:

See also: LOTR, Harry Potter, How to Train Your Dragon, Reign of Fire, etc, etc.

Left: Right temporal bone (endocranial view).
Right: Dragon.

So if you’re looking at a temporal bone in posterior view, you’ll see the petrous portion stretching anterio-medially towards the midline of the body. The internal auditory meatus (as indicated in the photo from White & Folkens’ HBM, above) is the dragon’s “eye”, while the carotid canal that opens inferiorly and medially is the dragon’s “mouth”. The large and smooth IAM foramen is only visible posteriorly, so if you examine the cranium from this aspect, the left temporal “dragon” and right temporal “dragon” appear to be facing each other – or, if it’s mating season, appear to be breathing fire at each other in a breath-taking demonstration of intrasexual competition, as in the depiction above.

Dragons are cantankerous creatures, aren't they?

Left: Dragon.
Right: Left temporal bone, (endocranial view).

Siding Tips: If you’re having trouble orienting an isolated petrous portion, one trick I always use is the position of the superior petrosal sulcus. This is a narrow but palpable groove that runs along the superior-most part of the petrous portion towards the squamous portion of the temporal bone (from the tip of the dragon’s snout along his entire head, if you will). Depending on how much of the bone you have, you can also use the position of the sigmoid sulcus (identified in the first photo by White), which is going to sit posteriorly and laterally relative to the petrous portion. It curves around the “neck” of the dragon – you can think of it as an excellent place to put a collar – or, you know, a transverse sinus.

Finally, let’s reward ourselves for learning about the temporal bone by taking a minute to celebrate the truly astounding grasp of the concept of evolution demonstrated by the masterpiece that is Reign of Fire. Don’t even get me started on why the inhabitants of a remote fortress in NORTHERN ENGLAND are practicing a form of subsistence farming that relies heavily on the cultivation of TOMATOES :

Original images found here: 1 & 2 & 3. First temporal bone photo from White & Folkens’ Human Bone Manual (2005), p. 97,

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