As part of an anatomy course, a group of four medical students had been dissecting the thorax of a cadaver. It had taken them a few weeks as they progressed step-by-step from the skin to a now almost empty chest cavity. The heart remained in place for the next phase of dissection but the lungs were not removed.
Upon completion of this stage in the process, the students were required to be assessed by a demonstrator who would check on their learning. The demonstrator for that group of students was me. I was duly called over to quiz them. What met me was an open, lung-less cavity with the anterior wall of the chest folded back. The lungs lay elsewhere on the dissecting table.
'Before we start,' I said, 'let's put everything back into its original place so we can go through what you've done step by step.' The students picked up the lungs, quickly looked at them and squeezed them into their respective cavities. Or so they thought.
The left and right lungs are not exact mirror images of each other. For a start, the heart is situated slightly to the left and so impinges upon the left lung. For this reason - or so it is usually stated - the left lung has just two lobes, whereas the right has three. (Whether that is the complete explanation, I do not know. Indeed, what follows may suggest that the explanation lies elsewhere.)
What the students did, before putting the lungs back into the chest, was count the number of lobes: two means left, three means right. The lungs being the spongy compliant organs could be squeezed in fairly easily. But then, lungs can be squeezed into almost any space - even those from embalmed cadavers.
With this body, I could tell, things were not as expected. The left lung had three lobes (not two); the right lung had two lobes (not three). The opposite of what the students had expected; the opposite of what they had been taught and what they had read. By simply counting the lobes the students had proceeded to squeeze each lung, into a cavity of the wrong shape and size - and facing backwards!
There are more accurate ways of determining to which side a lung belongs. These do not require the number of lobes to be counted. There are a number of clearly visible surface characteristics which allows the lung to be orientated in space.
I pointed out the error to the students and passed it off lightly. We were able to laugh about it and started again. The students passed the quiz. They were serious-minded people who had applied themselves diligently to their task. I am sure that their error was a useful learning experience. However, it was actually quite a grave mistake. It would even have resulted in failure under stricter conditions.
Significantly, this was the first time any of those students had realised this anomaly about their cadaver. None of them had noticed when the lungs were first removed that the number of lobes was atypical. How could they have missed something so glaringly obvious?
Being diligent students may have been their problem. They had followed the dissecting instructions meticulously. They had removed the lungs and put them aside for dissection later as instructed. They had proceeded to dissect the empty cavities left behind before focusing on the lungs as separate organs. When it came to examining the lungs, there was, as described one with two and one with three lobes. They had assumed - as stated above - two means left, three means right.
Were the students really at fault? They were following instructions; they were doing what they were required to do. They were not required to explore the human body or discover things about it for themselves. They were put into an environment in which instructions were to be followed. It may be little wonder that they slipped up. They were learning the contents of a prescribed syllabus. The cadaver they used was a means of simply backing this up when a spirit of discovery might have been preferable.
