Many of our readers have contacted us about our recent blog post (June 17, 2018), which describes a simple experiment for locating the center of gravity of a model skull. They have pointed out the major differences between a skull and a head. Their question is this: you’ve measured a skull, but do the skull and the intact head have the same center of gravity? A skull is a skull, after all, and nothing but bone. It lacks a brain, eyes, blood vessels, and fluid of any kind. All this soft tissue that we neglect in our experiment has mass--in fact more mass than the skull itself. Does the weight of the soft tissue change the distribution of weight in the head from that of the skull?
This is not an easy question to answer, as the head is not amenable to the kind of lay research described in our blog. It was a simple matter to hang our model skull from a string and trace plumb lines. Performing this experiment using an intact human head was, for us, impossible and undesirable. However, researchers in crash test laboratories have addressed this very question, developing elaborate preparations and methods to determine the center of gravity of cadaver heads. In a report submitted to the Office of Naval Research, Beier et al. (1979) calculated the average center of gravity of several dozen cadaver heads. They found an average location at “0.8 cm in front of the auditory meatuses and 3.1 cm above the Frankfort plane” (Beier et al, 1979, 21, 24), along the mid-sagittal plane. In plain English, this means that this point is on the midline of the skull, about an inch forward of the atlantooccipital joint, and another inch up from there. In other words, it's at the sella turcica. To read the report, follow this link. More recently, researchers have developed digital representations of the head and used them to make similar measurements. For an example, follow this link.
So it is a curious physiological fact that the center of gravity of the skull is the same as the center of gravity of the intact head.
We thank our readers for their input, and welcome your comments.