I previously mentioned the LOS (Lower Oesophageal Sphincter) and how once it had no place in the human anatomical canon but now does. What of things being the other way round? That is, are there any structures that exist in the human anatomical canon but not in the human body? If there is a candidate, it is the cisterna chyli. This is (supposedly) an expanded portion of the lower end of the thoracic duct where a number of lymph vessels converge, delivering their contents on the way to being returned to the circulation.
The cisterna chyli was first described in the 1650s by Jean Pecquet (1622-1674), a French anatomist whose work relied upon dissections using dogs rather than human cadavers. Notwithstanding this, the cisterna chyli went on to find its way into human anatomy texts. When eponymes were popular, textbooks of human anatomy often referred to it as the 'cistern of Pecquet' or 'reservoir of Pecquet'. There it has remained. However, it is not, in fact, a structure often found in humans.
Studies using human material suggest that the cisterna chyli may only be present in about 14% of individuals. (This I obtain from a footnote to the 35th Edition of Gray’s Anatomy.) A number of variants in the arrangement of the lymph vessels in the area of the lower thoracic duct/cisterna chyli are well known. In fact, the area is often highlighted as being one of considerable anatomical variability.
Surely, if the cisterna chyli is not present in the human body and that area is known for being very variable, how does it persist in the textbooks? Wouldn’t generations of medical students looking for it not point out to their teachers that it wasn’t where they were told to find it?
In my experience, generations of medical students dissecting the posterior abdominal wall and not finding it have blamed their poor dissecting skills rather than the textbooks and dissecting guides. Their teachers have similarly assumed these sources to be unerring and their students clumsy.
If correct, how does an occurance rate of 14% qualify something to be taught as canonical? When performing statistics on experimental data, 95% is the confidence level at which a result is deemed statistically significant. Occurring in the human body at a rate of 14% is well below 95% and hardly implies that it is ‘typical’ or ‘ordinary’… or canonical.
Note on Jean Pecquet
I once read that Pecquet’s particular research interest was the physiological effects of alcohol. In an era when investigators were not averse to experimenting on themselves, it appears that Pecquet did the same… and died of the effects of his own research.
