Monday, 28 October 2019

Bones bones bones

Each year, the same lab practicals come round regular like clockwork, or the appearance of the Perseids in August. I think I've finally nailed the count of bones in the human body. It is therefore an entirely appropriate time to hang up my lab-coat and give up my desk for a younger model. When you stop learning you may give up teaching. I've ranted before about how the PubQuiz answer to the count of bones in the human body excludes the 6 micro-bones in the ears which allow us to hear. I have not been correct in this high moral ground. But there are still inconsistencies in how Everyone comes to agree that adult humans have 206 bones. My Cell Biology class this year seems to be a little more engaged in the process than some groups in previous years. They were at least honest to the task because I made them park their smart-phones and think about how many bones they had about their person. It's okay to be wrong, I cried, it's the first step towards knowing. They all had different answers though, which is evidence of honesty, which is evidence that they have thought about it rather than acting as a know-nothing channel for Wikipedia.
I guess if I offered them €1 for each identified bone, then they'd work harder to get to 206 . . . without working too hard so that they fudge the answer to make it right. I've also included the official answer (from St Wiki of Pedia) of how the agreed N = 206 is arrived at. Compared to my last attempt at this exercise.
Axial = 80 (8+14+7+26+25)
  • Cranium N=8: occipital bone, 2 temporal bones, 2 parietal bones, sphenoid bone, ethmoid bone, frontal bone
  • Face N=14: 1 vomer, 2 conchae, 2 nasal bones, 2 maxilla, 1 mandible, 2 palatine bones, 2 zygomatic bones, 2 lacrimal bones
  • Extras N=7: hyoid, ears: 2 stapes, 2 malleus, 2 incus
  • Vertebrae N=26, 7 cervical,12 thoracic, 5 lumbar, 1 sacrum, 1 coccyx
  • Ribs+sternum N=25
Appendicular = 126 (10+10+54+52)
  • Shoulder and arms N=10: 2 each scapula, clavicle, humerus, ulna, radius
  • Pelvis and legs N=10: 2 each innominate, femur, patella, femur, tibia
  • Hands N=54: 16 carpals, 38 metacarpals and phalanges (thumb only 2 phalanges)
  • Feet N=52: 14 tarsals, 38 metacarpals and phalanges (great toe ditto)
Thus N=206 only works if you decide to say
  • fused sacrum = one bone 
  • fused coccyx = one bone 
  • fused innominates / pelvis = two bones, one left, one right
  • fused mandible = one bone
  • fused skull = twenty-two bones + two each of malleus incus and stapes rattling around inside the ears = six
Which seems super arbitrary to me. I don't care how many bones there are in your body because it is GDPR personal and also very likely to be different from my tally. So much polymorphism in the lumbar, sacral and coccygeal vertebrae even before fusions start. So many ossicles "sesamoid bones" in the feet and at the base of the thumb which don't count though they are bigger than the distal phalange of the baby toe which does count. That's before we start on cervical ribs, polydactyly, thalidomide and Oscar Pistorius. About 206 but it depends on your definitions will do nicely

But we really must pull each other up on is bold statements like The adult human skeleton is comprised of 206 bones when the person expressing this Certain Knowledge literally doesn't know what they're talking about because they have as much difficulty as me reconciling that number to the inventory.

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