September 23, 2014
Here’s a thing I put together to help my students understand the many branches of the internal iliac artery in humans. In the image above, we’re looking in superomedial view into the right half of the sacrum and pelvis. Bones are white, ligaments blue, the piriformis muscle sort of meat-colored, and arteries red (for a tour of the pelvis identifying all of this stuff, see my pelvic foramina slideshow). At the top is a big inverted Y-shape: the common iliac arteries branching from the abdominal aorta, which continues on, much reduced, as the median sacral artery. The right common iliac artery is shown bifurcating into the external iliac artery, which continues on out of the pelvis to become the femoral artery, and the internal iliac artery, source of much fear and doubt.
The first thing to understand is that any particular branching pattern of the internal iliac arteries, whether in an anatomical altas, a lecture, revealed in a dream, or even in your own body, will probably have no bearing whatsoever on the branching pattern in the next person you encounter, alive or dead. Furthermore, the variation between right and left in a single person can be as great as that among different people. The branches to pelvic viscera are particularly fiendish; they sometimes travel far into the pelvis as a common trunk and then “starburst” near their target organs, making identification almost impossible. Do not waste your time trying to memorize any particular branching sequence. Instead, concentrate on matching the arteries to their targets; you will discover the identities of the branches by seeing where they are going, not the order in which they branch.
There are typically 10 named branches of the internal iliac artery. Authorities quibble on the details, as we’ll see in a moment, but if you know these 10, you’ll be fine for almost any conceivable purpose. A simple scheme of my own devising for remembering them is 2-4-4:
TWO to the back body wall:
- iliolumbar A—may arise from external or common iliac AA; sometimes double
- lateral sacral A—note branches to anterior sacral foramina and anastomoses with median sacral A
FOUR leaving the pelvis entirely:
- obturator A—often arises from the external iliac A instead, exits pelvis through obturator canal
- superior gluteal A—exits pelvis through suprapiriform foramen
- inferior gluteal A—exits pelvis through infrapiriform foramen, with internal pudendal A
- internal pudendal A—exits pelvis through infrapiriform foramen, with inferior gluteal A
FOUR to pelvic viscera:
- superior vesical A—usually the dominant artery of the anterior trunk, this is the patent part of the obliterated umbilical artery, which survives as the medial umbilical ligament
- inferior vesical A (males) / vaginal A (females)—may branch off uterine A (females) or superior vesical A (both)
- uterine A (females)—major artery to uterus, approaches laterally within the broad ligament
A to ductus deferens (males)—extremely small and difficult to trace
- middle rectal A—usually the most inferior branch of the entire internal iliac tree (at least inside the pelvis)
My way to explain those last four is to extend my index finger and say, “Everybody has to pee, so up front we have superior vesical.” Then extend my pinky and say, “And everyone has to poop, so in back we have middle rectal.” Then extend digits three and four and explain that the identity of the middle two arteries varies between the sexes (but that the inferior vesical artery of males and the vaginal artery of females are basically the same vessel).
There is a LOT of variation in the descriptions of the internal iliac artery branches among different sources — almost as much variation as there is in the arteries themselves.
- The Thieme Atlas of Anatomy, 2nd Ed (Gilroy et al. 2009), Table 19.1 on p. 254, includes the inferior vesical artery for both sexes. The artery to ductus deferens is listed as a branch of the superior vesical artery, and the uterine and vaginal arteries are listed separately, bringing the total for females to 11.
- Clinically Oriented Anatomy, 7th Ed (Moore et al. 2013), Table 3.4 and pp. 350-355, lists the 10 branches I went through above. Moore et al. explicitly say that the vaginal artery is the female homolog of the inferior vesical artery (p. 351).
- Gray’s Anatomy, 40th Ed (Standring et al. 2008), pp. 1085-1089, splits the difference. The artery to ductus deferens is not listed; instead, the ductus deferens is said to be supplied by the inferior vesical A (in contrast to Thieme, which has it is supplied by the superior vesical A). Both the vaginal and inferior vesical arteries are listed, but the vaginal artery is said to frequently replace the inferior vesical artery.
The upshot is that pretty much all of these sources agree on how the blood is getting distributed, there are just some minor differences over what we call certain vessels. I have never personally seen a dissection detailed enough to allow an interior vesical artery to be recognized separately from the vaginal artery — the vagina lies so close behind the bladder that whatever you call the artery that runs lateral to them, it could easily be supplying both structures, and probably does. As far as I’m concerned, the inferior vesical artery in males and the vaginal artery in females are the same artery, in that they both supply the inferior portion of the bladder. I think it’s just a historical hiccup that we call them by different names, possibly perpetrated by smelly, lonely, vagina-obsessed men of centuries past.
A final note, added in revision: some sources refer to two trunks or divisions of the internal iliac artery: a posterior trunk that gives rise to the iliolumbar, lateral sacral, and superior gluteal arteries, and an anterior trunk that gives rise to everything else. If that’s what your professor tells you, smile and nod and keep your heretical thoughts to yourself. Personally, I regard the notion of trunks of the internal iliac artery alongside phlogiston, luminiferous aether, and snorkeling sauropods, as romantic nonsense at best. I have seen an obturator artery arise from a superior gluteal artery and a pudendal artery arise from a superior vesical artery. In a world where variants like those can and do turn up frequently, the stability and reason implied by regular trunks is illusory.
- Gilroy, A., MacPherson, B., and Ross, L. (eds.) 2009. Atlas of Anatomy, 2nd ed. Thieme, Stuttgart.
- Moore, K.L., Dalley, A.F., and Agur, A.M. 2013. Clincially Oriented Anatomy, 7th ed. Lippincott Williams & Wilkins, Philadelphia.
- Standring, S. 2008. Gray’s Anatomy, 40 ed. Churchill Livingstone, London.
September 18, 2014
There is little enthusiasm for CC-BY [...] in the field of political studies. [...] It is clear that there is serious concern about the potential for work published under a CC-BY licence to be distorted and used inappropriately.
There may be concern, but it’s misplaced. Using CC By does not allow your work to be misrepresented. The human-readably summary of the licence clearly states, in its definition of the attribution clause: [Emphasis added]
You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
What does this mean? It means creationists can’t take our paper on sauropod neck anatomy, change it so that we seem to be advocating Intelligent Design, and post the result as though it’s our work. Instead, the terms of the licence require that they state that changes were made, and that they do not portray us as endorsing their use.
Really, I don’t see how much clearer or simpler the CC By licence could be. It’s 108 words long. For heavens’ sake, folks, go and read it. It’s ridiculous that we have academics, who are supposed to be trained in research and rigour, expressing flagrantly incorrect opinions about a hundred-word-long document that they’ve not even read.
September 17, 2014
I’ve always thought of SVPCA as a pretty well gender-balanced conference: if not 50-50 men and women, then no more than 60-40 slanted towards men. So imagine my surprise when I ran the actual numbers.
1. Delegates. I went through the delegate list at the back of the abstracts book, counting the men and women. Those I knew, or whose name made it obvious, I noted down; the half-dozen that I couldn’t easily categorise, I have successfully stalked on the Internet. So I now know that there were 39 women and 79 men — so that women made up 33% of the delegates, almost exactly one third.
2. Presentations. There were a total of 50 presentations in the three days of SVPCA: 18 on days 1 and 3, and 14 on day 2, which had a poster session in place of the final session of four talks. I counted the presenters (which were usually, but not always, the lead authors). Here’s how the number of talks by women broke down:
Day one: 2 of 18
Day two: 8 of 14
Day three: 3 of 18
In total, this gives us 13 of 50 talks by women, or 26%.
3. Presenter:delegate ratios. Since 37 of the 79 attending men gave talks, that’s 47% of them; but only 13 of the 39 attending women gave talks, which is 33%. On other words, a man attending SVPCA was 40% more likely to give a talk than a woman.
I’m not sure what to make of all this. I was shocked when I found that only one ninth of the first day’s talks were by women. It’s a statistical oddity that women actually dominated day two, but day three was nearly as unbalanced as day one.
Since SVPCA accepts pretty much every submitted talk, the conference itself can’t be blamed for the imbalance. (At least, not unless you think the organisers should turn down talks by men just because they’re men, leaving blank spots in the program.) It seems that the imbalance more likely reflects that of the field in general. Maybe more disturbing is that the proportion of women giving talks was rather less than the proportion attending (26% vs. 33%) which suggests that perhaps women feel more confident about attending than about presenting.
It would be interesting to know how these numbers compare with SVP’s.
September 2, 2014
A couple of weeks ago, more than hundred scientists sent an open letter to the AAAS (American Association for the Advancement of Science) about their new open-access journal Science Advances, which is deficient in various ways — not least the absurdly inflated article-processing charge.
Today I learn from email that there has finally been a response — of sorts. Editor-in-Chief Marcia McNutt had a long phone-call with Jon Tennant — one of the hundred-plus authors/co-signers. All we know about that call is (and I quote from Jon’s email account) “it became quite apparent that we would have to agree to disagree on many points”.
All I want to say is this. When a hundred scientists co-sign an open letter, it is TOTALLY UNACCEPTABLE for the response to take the form of a private telephone call with one of those authors.
Come on, AAAS. This is all about openness. Let’s see an open response: a substantive, non-patronising one which addresses the actual points made in the original letter.
Meanwhile, you may like to read this article at The New Statesman: Scientists criticise new “open access” journal which limits research-sharing with copyright. In finishes on this very clear note, courtesy of Jon Tennant:
The AAAS should be a shining beacon within the academic world for progression of science. If this is their best shot at that, it’s an absolute disaster at the start on all levels. What publishers need to remember is that the academic community is not here to serve them – it is the other way around.
August 28, 2014
I’m scrambling to get everything done before I leave for England and SVPCA this weekend, so no time for a substantive post. Instead, some goodies from old papers I’ve been reading. Explanations will have to come in the comments, if at all.
For more noodling about nerves, please see:
- The world’s longest cells? Speculations on the nervous systems of sauropods
- Oblivious sauropods being eaten
- Butler, A.B., and Hodos, W. 1996. Comparative Vertebrate Neuroanatomy: Evolution and Adaptation. 514 pp. Wiley–Liss, New York.
- Nieuwenhuys, R. (1964). Comparative anatomy of the spinal cord. Progress in Brain Research, 11, 1-57.
- Streeter, G. L. (1904). The structure of the spinal cord of the ostrich. American Journal of Anatomy, 3(1), 1-27.