I ask because there is indeed a good physiological reason for asking. The human eye is indeed much more sensitive to horizontal lines
than vertical ones. This is probably atavistic. We are descended (it seems) from savannah-dwelling bipeds, who were only rarely tree
climbers, unlike the chimpanzee, orang-utan or lemur families of the great apes who remained mostly arboreal. The horizon is therefore a
feature that is present at all times, and thus noticing a perturbation of that smooth (tautologically) horizontal line would confer a
powerful evolutionary advantage if it found moving prey or predators.
Thus, we are more likely to see horizontal lines than vertical ones. John's comment that he turns X-rays to the orientation in which they
were taken to see fluid levels is simply another way of making the same point. It is interesting that frequently missed fractures are all
vertical when X-rays are viewed in standard orientation. Radial neck fractures, pubic ramus fractures and occipital skull fractures will
all appear vertical in standard radiographs, and are all readily missed by the tyro. I therefore recommend that X-rays are viewed in the
orientation which makes the expected abnormality approximate to a horizontal line where possible.
Best wishes,
Rowley Cottingham
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