A nutrient foramen is a small, smooth-walled hole for blood vessels found on the external surface of a bone. Size-wise these tend to be in the range of what you’d expect if you poked the tip of a pen through the bone itself, especially for the largest foramina that appear on long bone shafts. There’s some variability to the locations of nutrient foramina, particularly on irregular bones, though on long bones they’re almost always found on the shaft.
Fortunately, the directionality of the apeture itself is a constant that you can use to help orient long bone shafts, even if the proximal and distal ends are broken off. Generations of osteologists have even taken the time to distill their knowledge into one strikingly memorable line of verse, right up there with “Had we but world enough and time” or “Turning and turning in the widening gyre”. To orient a fragmentary long bone shaft, all you have to do is repeat the mantra that nutrient foramina “go to the elbows, and flee the knees“, which is catchy enough that you don’t even need to be into the metaphysicals or modernists to remember it.
I always find thinking about what direction a needle would point if I stuck it into the foramen to be a useful trick. In the case of the tibia below, the tip of the needle is “fleeing the knees”, or pointing distally, a trait that would allow you to side this bone even without access to a larger portion of the shaft.
Image Credit: Sewing needle found here. All photos of bones taken at the Museo de Jaén, summer 2014.
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big fan of bones