Death's Acre: Inside The Legendary Forensic Lab The Body Farm by Bill Bass (essential books to read txt) 📕

holding the right femur. I laid it on the grass, adjoining an imaginary hipbone. Somewhere in between I mentally pictured a pelvis, a spinal column, two arms, and the rib cage. At the top of the imaginary spine I laid the head and mandible.

The face was gone. Leering up at us from the grass was a greasy, stained skull with rotting patches of skin and muscle at the sides and back of the head. For a bone man like me (this was years before the term forensic anthropologist was coined), the absence of flesh on the face would actually simplify our task.

Here’s why: A corpse’s skin can be deceptive. If a body is bloated, the facial tissues can swell, making it more difficult to discern the person’s gender. If the genitals are missing—because of dismemberment, decomposition, putrefaction, or animal feeding—or the soft tissue is badly decomposed, the shapes of the bones themselves will offer the most reliable information.

This particular skull was small, which immediately suggested either a child or a woman. The mouth was narrow and the chin was pointed—additional features characteristic of a woman. The forehead was gracile—smooth or streamlined, particularly the forehead and the ridge above the eyebrows: a textbook example of a woman’s skull, I told the students.

“You’ve probably seen cartoons of big, hulking Neanderthal cavemen,” I said. “The men have these massive brow ridges, so that when another caveman clubs them with a woolly mammoth femur, it doesn’t hurt.” They laughed at that; over the years I’ve found that humor helps students learn, so I always look for opportunities to throw in jokes that will reinforce what I’m explaining. “I’m not saying that we men have failed to evolve in the last twenty thousand years, but a modern male skull looks a whole lot more like a Neanderthal’s than a modern female skull does.”

Holding the skull up so they could see it better (and smell it better, too, unfortunately), I showed them the brow ridge above the eyes. Lacking the massive ridge of the male, a woman’s skull has sharp edges where the eye orbits, or sockets, are set beneath the forehead. Finally, turning the head around, I showed them the base of the skull—the occipital bone—where men have a bony bump called the external occipital protuberance. This skull didn’t; clearly this was not a manly man.

“But how can you tell for sure,” I asked the students, “whether this was an adult woman or a twelve-year-old boy?”

One of the students hazarded a guess: “The teeth?”

“That’s right,” I said, “the teeth.”

Our mystery victim had a full set of teeth—thirty, including the upper pair of third molars, or wisdom teeth, though not the lower pair. One evolutionary change we humans are undergoing as we’ve given up gnawing on animal bones is the gradual loss of our third molars. Some people’s wisdom teeth never erupt; they’re like a seed that never germinates. So, finding a skull in which the third molars haven’t erupted, I explained, doesn’t necessarily mean that the person was not yet an adult. However, if the third molars have erupted, I stressed, it’s virtually certain that the individual was eighteen or older. In this case, then, I was pretty sure we were looking at an adult woman.

The best way to confirm that, I added, would be to examine the pelvis. It was a shame we didn’t have it.

The adult pelvis is a complexly engineered structure resulting from the union of three rugged bones: the sacrum, at the base of the spinal column, and the two hipbones, the right innominate bone and the left innominate. (The term innominate, which translates as “nameless” or “unnamable” bone, is a comment on its odd shape: Viewed from the front, the hipbones flare out like the ears of an angry elephant; underneath those flaring, bony ears are two knobs pierced by openings like empty eye sockets; in front, two prongs of bone converge like tusks grown badly awry.)

The sacrum acts as a weight distributor, splitting the weight from a single column, the spine, into two columns, the legs, by way of the right innominate and the left innominate. But the innominate itself is a complicated structure, somewhat analogous to the cranium, which is also formed by the fusion of multiple bones.

Before puberty, each innominate bone consists of three separate bones: the ilium, the ischium, and the pubis. The ilium is the highest, broadest part of the hipbone; its crest is what flares out like elephant ears just below the waist. The ischium is the bony structure you can feel yourself sitting on, if you wiggle your butt on a hard, wooden chair. (Some of us have a hard time feeling anything bony inside that big blob of fatty tissue, but it’s there nonetheless.) The pubis is the bone that spans the front of the abdomen, about four inches or so below the navel.

At puberty the pelvis gets interesting in many ways, including skeletally. To allow passage of a baby’s head during childbirth, the female’s hipbone gradually broadens and the pubic bone gets longer, angling farther forward to form more of an arch for the birth canal.

Because the male’s pelvis is markedly narrower, his femurs hang roughly straight down below his hipbones. In an adult female the femurs incline slightly inward beneath the hips. Not surprisingly, this difference in pelvic and femur geometry translates into some scientifically observable and aesthetically pleasing differences in the way men and women sit, stand, and walk.

In the case of our recently unearthed murder victim, then, having the pelvis would have easily confirmed that the skull was a woman’s.

The pelvis would also have told us more about our victim’s age. Like the sutures in the skull, the joint at the body’s midline where the left pubis meets the right pubis—called the pubic symphysis—is an excellent yardstick for measuring age. From late adolescence through about age fifty or so, the bony face of the pubic symphysis undergoes a gradual, consistent set of changes, which were first studied and