A/N: Let me say first, as a disclaimer, that I have absolutely no real knowledge of the human skeleton. Everything you read here has been gleaned from about thirty different websites, the most prominent being Wikipedia. If you spot any mistakes, please let me know.

Oh, and perhaps I should add that I don't own Sherlock.

"He knew the anguish of the marrow

The ague of the skeleton;

No contact possible to flesh

Allayed the fever of the bone."

- Whispers of Immortality, T.S. Eliot.

.

There are two-hundred-and-six bones in the human body. Sherlock can name them all.

He can tell you that the largest bone in the body is the femur in the thigh and the smallest is the stapes bone, deep inside the ear. He can tell you that in an adult, the skeleton comprises around thirty to forty per cent of the total body weight, and half of this weight is water. He can tell you that bones have eleven main functions and list them all, including the names of the chemicals they produce.

It's a fascination he has had all his life, one that has fit so seamlessly into the skills needed for his work that he barely thinks about it. There is so much data to be read in the formation of the skull, the shape of the hands, the long-healed fractures of the radius or humerus. He scatters bones like the soothsayers of old and reads their history. He knows their names. He studies how they fit together, the articulation of muscle and sinew. He watches them move beneath the skin, finds himself staring at his flatmate as he moves about their shared space and slowly, slowly, he realises John's bones are beautiful.

Sherlock does what he always does when presented with a problem. He collects data.

.

.

Sherlock has had the skull as long as he has had his business. When he began, in a one-room bedsit throttled by damp, the skull was the only piece of furniture he owned. It has lost several teeth over the years, and its mandible is held on with wire, but he has carried it with him like an old friend.

He still talks to the skull but the hyoid bone, the horseshoe-shaped bone that supports the tongue, is long lost. It can no longer talk back.

The skull lives on the mantle when it is not in his hands. Sherlock likes to feel the smoothness of the plates underneath his palm, to cup the crown, to slide his hand forwards to the curve of the eye socket and thread his fingers through as you would a bowling ball. Sometimes he scratches gently at the inside of the cranium; his fingernails have left shallow grooves in the parietal plate. On his bad days (when his head is filled with white noise and his there is no data and his mind rebels at stagnation) Sherlock fancies that if they were to crack him open his skull would bear those very same marks.

John's skull is radically different. It is smaller, for one, and rounder. John has little by way of cheekbones but this is somehow intriguing, like a buried secret. Sherlock dwells instead on the hollows of John's temples and the bridge of his nose and his sharp, sharp teeth. He watches John grit his teeth in frustration and follows the way the skin pulls tight, throwing his jaw sharply into relief. He will run his thumb along the jawbone of the skull in his hands as his eyes trace the sweep of bone up to the hollow beneath his earlobe and beyond, to the sheltered ridge behind his ear—but instead of cartilage his fingertips brush wire. He must turn the skull over, imagine running his fingers through John's hair and down, cupping the base of his skull, passing the vulnerable point where occipital bone meets vertebrae (the first cervical vertebrae is called the Atlas and it articulates skull to backbone and Sherlock is aware that many would find this poetic) and on to the rocky ridges of the spine.

The human skull is as unique as a fingerprint. It is possible, given accurate knowledge and the right software, to rebuild the facial features of its owner long after the flesh has rotted away. Sherlock does not need this. He could pick out John's skull from thousands.

.

.

John's hands, his small, quick, capable fingers (made up of carpals metacarpals phalanges [proximal middle distal]), the pale pink shells of his fingernails (they are not made of bone, they are made made of keratin like his hair but they enthral him anyway, he would bite them for John if he could) his pale, delicate wrists(ulna, ulna, it rolls off the tongue), glimpsed rarely above the glove of his tan-line—these are familiar to him in a way nothing else is.

There is a phrase Lestrade uses occasionally; he says Sherlock knows London "like the back of his hand", but Sherlock thinks perhaps he knows the backs of John's hands better than his own, better than London.

John is doing the washing-up. The sleeves of his jumper are rolled high, just above his elbows. Sherlock watches John's wet hands as he looks for a tea towel, imagines licking dishwater from the hills and valleys of John's knuckles. John's hands curl into fists and then into bright stars as he tries to flick the water away, but rivulets run down his forearms, bead on his elbow and drip to the floor.

And just like that, John's elbows become the most erotic thing Sherlock has ever seen.

.

.

There are twenty-six bones in the human foot, one less than in the hand. This is a fact Sherlock finds endlessly perplexing. That John's hands, with all their skill and flexibility, the endless combinations of muscle manipulation that allow him to make a fist, sew a wound, pull a trigger, type, clap, twiddle his thumbs and carry several empty cups at once should only be one bone better than his feet is baffling. Feet are not an attractive part of the anatomy. They are half-formed things, a snapshot of evolution at work, caught between the appendages they were and whatever they will become. They remind Sherlock of the pale roots of vegetables buried deep, and they repulse him.

Until John walks in one evening barefoot, arms full of washing. Sherlock watches his toes wriggle in the carpet like roots searching for earth and expects to feel revulsion. But he doesn't. Instead he observes, fascinated, as John feels about the floor with his foot for a sock he has dropped, hooks it between his toes and passes it deftly into his outstretched hand. John's pyjamas are slightly too short for him, and Sherlock's eyes follow the rounded nub of John's ankle and the push and pull of tendons until John disappears down the stairs.

Sherlock is reminded that the human foot is one bone away from the human hand, and is awed.

.

.

One day John reaches for a mug on the top shelf of their cupboard. Sherlock thinks of those hipbones bucking against the palms of his hands for days.

.

.

The upper seven ribs of the ribcage are called the "true ribs".

The eighth, ninth and tenth are called the "false ribs".

The eleventh and twelfth are called the "floating ribs".

The floating ribs do not have any connection to the sternum, and these are the ones to aim for in hand-to hand combat. Sherlock knows this from first-hand experience.

About one in two- to five-hundred people have an additional cervical rib. Sherlock knows this from a case he took on a year ago.

The circumference of a normal adult ribcage expands by three to five centimetres during inhalation. Sherlock knows this from looking at John.

John breathes in, and his ribs press out, against the skin, the seventh to the twelfth visible. If Sherlock were to place his hands against John's sides he could feel them appear and disappear with John's breaths, like a magic trick. The individual ribs are not named but Sherlock assigns them all notes, imagines plucking out chords and arpeggios, strumming across the very heart of John. He could monitor John's respiration this way, by the bones that flex beneath his fingers as John's breaths become harsher and faster. Appear, disappear. Appear, disappear.

John looks up from where he is frantically trying to iron his shirt before work. His sharp sharp teeth are clamped around a piece of toast. The gentle hollow of his throat turns his collarbones into an accolade or brace, a mark used to indicate two or more lines of music to be played simultaneously. His hipbones are a closed bracket.

Sherlock longs to play John.

.

.

The skeleton has many functions, one of which is to provide protection for the vulnerable parts of the body. Brain. Lungs. Heart.

It is this Sherlock thinks of when he wanders into the living room during the elastic time between midnight and four to find John, hunched over in the middle of the floor in front of the TV. His eyes full of blood and sand. He has drawn his knees up to his chest and enclosed them within his clasped arms to leave no soft parts visible. There is a blanket pooled on the floor. He does not look up when Sherlock comes in, or when the kettle starts to boil, not even when Sherlock presses a mug of tea into his hands and folds his considerable frame beside John.

The silence between them is thick and heavy and somehow fragrant, like incense or lily of the valley. John is still, so still, painfully still; he has drawn back inside of himself, retreated to the place behind his eyes. He holds his left arm awkwardly. When Sherlock's hand alights softly on his shoulder he nods, resigned.

Sherlock slips behind him like a shadow. John's neck bends forward slightly to allow a better view of his scar, and Sherlock's breath dies in his throat. From here he can see, for the first time, the vast plain of John's back, the mountain range of his spine that snakes down to disappear below the waistband of John's pyjamas. There are thirty-three vertebrae in humans and Sherlock thinks he can see a great deal of them, but the TV flickers too fast for him to focus and he'd need his hands to count. John's clasped arms throw his shoulder blades (the scapula, an ugly word) into sharp relief, and Sherlock watches them press against his skin like wings trying to escape.

Sherlock desperately tries to ignore the flexing of John's ribs (appear, disappear, appear, disappear) and focuses instead on twisted knot of tissue at John's shoulder, the exit wound. His fingers probe the scar with surgical precision, creating a ballistics report as he moves along. He catalogues the calibre of the bullet, the angle at point of entry, estimates roughly the amount of time it would have taken to heal—but for once he does this silently, because John knows it all already. Gently he presses one finger (smallest amount of surface area possible, he is not made of stone) into John's spine and he arches his back obediently. Dizzy, Sherlock runs the pad of his thumb across the blunt edge of John's scapula, then again to be sure. There is a tiny flaw there, unnoticeable unless you were looking for it, hidden beneath the scar tissue.

"The bullet…" but his mouth is dry and he cannot finish.

"Missed the main artery. Took a chip out of my shoulder blade, though," says John, craning his neck to look at Sherlock. He frowns. "Are you—"

But it's too much, and Sherlock lets out a deep, shuddering breath, and presses his mouth to John's sixth vertebrae.

And then suddenly John is twisting in his arms, all corners and edges and sharp, sharp teeth. The kneecap is called the patella and it is the largest sesamoid bone in the human body and it is pressing into Sherlock's thigh as John's mouth meets his. Sherlock's hands skitter to cup John's shoulder blades; he feels the scapula unfold against his palms like the beating of wings.

One primary use of the skeleton is to serve as a frame upon which the entire body is built. Another is to allow movement via the manipulation of muscles, tendons and joints. Sherlock has watched John move for months but now the slightest twitch captivates him; John shifts, and it's like the movement of tectonic plates. Sherlock stretches John out like a map, learns his topography with his hands and mouth. John is soft and hard in the most unexpected of places, and Sherlock tries his best to learn his hills and valleys, the bluff of his collarbones, the summits of his elbows and knees. Sherlock wants to explore John until he knows his body like the back of his hand, like the back of John's hands, like London. He grips tight and and John grips back, until they are fused together so completely that if it weren't for all the flesh and muscle and skin they'd be one skeleton. Together they could baffle scientists. Their hipbones slip together and the groove of one's ribcage was made for the other and somewhere in the night Sherlock finds himself thanking evolution for John's hyoid bone.

(Sherlock's favourite bone is at the base of the spine, just above the coccyx; it is called the sacrum, meaning sacred. When Sherlock presses his mouth here, John comes undone.)

Much, much later, when they are sleepy and soft and far too tired to move, Sherlock reaches out a hand for John, and their metacarpals knit together into a perfect knot of flesh and bone.

When we die, thinks Sherlock, they can bury us in the same grave, and once our flesh decays they won't know whose bones are whose.

.

.

There are parts of John that Sherlock can never see. The humerus, the femur, the fibula, several vertebrae, parts of the pelvis—these are buried too deep below the surface. Sometimes Sherlock lies with John and simply touches him, murmuring John's Latin names under his breath. Every now and then there is a blank space where the skeleton simply disappears, and Sherlock, frustrated, has to pick up the map elsewhere. Whenever this happens John takes Sherlock's hand and places it on his hip, or his knee, or his eighth rib. "Name me," he says.

Several weeks into their relationship, John comes home from the hospital with a large file in his hands. Inside is an inch-thick sheaf of x-ray and MRI images of John's entire skeleton.

There are two-hundred-and-six bones in John's body. Sherlock can name them all.

.