Anatomy of the Soul

In fiction, especially of the magical kind, human anatomy ain't got nuthin' on the anatomy of a soul. And hearts. And minds.

So just how many 'pieces' is a normal human's soul made up of? What do they represent, and what happens if one gets lost or stolen? That is what this trope is about.

There are three basic components for a human's soul, without which the soul cannot live or even exist:
 * Spirit / Life Energy -- Pretty self explanatory. If the Body is an engine that the Mind drives, then the fuel is the Spirit. Those who want it do so for Immortality Immorality. Its loss may manifest as Rapid Aging, becoming very sickly or just plain death.
 * Mind -- The seat of consciousness; the logical, thinking, planning decider. Generally, it's biologically based, but the number of Freaky Friday Flip stories out there implies otherwise.
 * Split Personality -- Well, not so much a part of the mind as a mind apart. Split Personalities come in lots of shapes and sizes, but each generally represents a part of the character as a whole.
 * Inner Genius -- The conscience, essentially. Usually manifests as a Good Angel, Bad Angel, Spirit Advisor of some kind, the owner's Divine Spark that can do magic, or as a "wizard's familiar." Sometimes all of these at once.
 * Body -- Last but not least, the body serves as the vessel for all of these things. However, not all bodies are created equal, and there are dangerous things out there that want a human body so they can wreak havoc and indulge their vices. Some are simply incapable of being used for some truly powerful souls, usually ending in either the destruction of the body or forcing the soul to lose a lot of its power.

Other components for a human's soul can include:
 * Heart -- Generally, it's almost always the core component of the soul (hence the name; sometimes it's even what's meant with "soul", with the greater whole being called "spirit" instead), and also the one that is capable of love and emotion. Heart is also attributed with the nature of motion and the activity of life. It is usually the Morality Chain of a person, and usually carries all good and bad karma... unless those are separate components. It also bears the part of a human that can create life and art. Its loss can have varying effects, turning people into cold, dead husks, evil monsters, or brings Creative Sterility, unless the heart was deliberately removed for putting into a Soul Jar, however, whereupon the usual result is some form of Immortality instead.
 * Light -- If a heart has parts, expect them to be Yin and Yang. The "Light" half usually represents the positive, caring aspects of a person. Its loss will usually make someone a very... dangerous person to be around, if not at least very unpleasant.
 * Darkness -- Oddly, the "Dark" half isn't a good thing to lose either. It's not always evil, and generally contains all those useful survival instincts that turn to mushy pink feelings if it's absent. That said, an empowered dark side generally leads to a Super-Powered Evil Side and release of The Heartless.
 * Dreams -- Believe it or not, Dreams are a valuable commodity. All you need is a few days of insomniac nightmares to realize the value of even the most mundane dream. Supernatural creatures seem to treasure human dreams a great deal. Perhaps they can't dream? More majestically, a character's dream's represent their hopes and aspirations, so their loss represent a loss of drive and ambition. Perhaps more dangerously, the ability to sleep.
 * Karma/Destiny -- A tough aspect to show for western audiences. A character's Karma represents what they will become, their Destiny. So losing it usually means they're either doomed to an unremarkable life, or Immune to Fate.
 * Essence / True Name -- A philosophical and metaphysical concept that more or less is what makes something what it is. Both people, animals, and even inanimate objects have this. It's not usually directly named or addressed in fiction but a lot of stories reference it indirectly. Especially when related to magic systems that draw power from souls (or maybe even elements and nature). It's a connection with Essence that basically gives people the power to draw power from things because it defines what something can do and can become.
 * Shadow Archetype -- Everything a person rejects or denies about themselves, which they will often project upon others. Modern fiction equates it to evil, because Shadow Is Dark and Dark Is Evil, but the original Jungian concept can also contain positive aspects. Essentially, a Saint's Shadow will be a Sinner, and a Sinner's Shadow will be a Saint, but that's an oversimplification at best.

The loss of any one of these is never a good thing... usually. Someone who is carrying around a demon, Super-Powered Evil Side, or Split Personality will most likely benefit from having it removed. However, the case is usually that when any one of these is removed, the person becomes metaphysically incomplete. Their eyes hollow out, their conscience vanishes, and they operate on only the formalities of human behaviour, having lost either the empathy, will, or self control necessary to function as a human being. Expect reactions ranging from listlessness to displays of pure Id induced debauchery, or conscience and soulless killings.

Whoever possess one of these items usually gets one of the following: partial or total control over the owner, the ability to see their dreams, memories, or other secrets. If what they stole is replacing their own stolen or damaged goods, they usually gain at least part of the personality or morality of the owner. Then again, the nefarious Evil Sorcerer who stole it may be collecting enough 'raw materials' either to extend their own life, or looking for just the right one to perform some heinous evil ritual. Of course, it might be their own soul or heart that they discarded to avoid all those "limits" a conscience (and mortality) imposes.

There is an interesting possibility of a Yin-Yang Bomb if someone loses one of the above; learns abilities/powers that are granted in some kind of Equivalent Exchange / Disability Superpower and then they gain the lost soul part back. A risky method; and definitely uncomfortable; you're going to need loads of Heroic Willpower for this.

If the stolen, damaged, or corrupted component isn't returned in time, you can expect the owner to either wither and die, go into a catatonic coma, or be incurably evil/homicidal. If the stolen/removed item is left loose, it may become The Heartless, a Living Memory or even a Ghost whose body yet lives.

Anime and Manga

 * Sailor Moon featured quite a few of these, up to and including Life Energy, Dream Mirrors (a combination of ambition and the ability to dream and sleep and the former trope namer), Pure Heart Crystals (the emotional heart), and Star Seeds (the soul which allowed for reincarnation).
 * Removing them has various effects. Energy loss simply is just that, a loss of energy. Losing a Pure Heart puts the victim in a zombiesque or hysteric state. Most just collapse though. Removing the Mirror doesn't really do much but does cause pain to the victim if someone looks inside (by sticking their head INTO it); however, eating the Mirror will cause the victim to die if it is not recovered. The Star Seed will cause a person to fade away if taken far away or if the person is a Sailor Senshi (due to it doubling as a source of their powers). If it's a normal person and it remains close by it will turn them into a Phage or Fake Sailor Senshi (even men).
 * The Dream Mirror also came in three kinds, a normal pink one, a dark grey one for someone who's given up on their dreams, and a golden one that indicates Pegasus is hiding in it.
 * Star Seeds also come in two types, blanks which are held by normal humans and true Star Seeds which are held by Sailor Senshi (and Tuxedo Mask) and are the anime equivalent of the manga's Sailor Crystal.
 * The duality of dream mirrors probably exists because the Japanese word "yume" covers both meanings of the English "dream": sleep visions and fantasies/aspirations. It was trickier to carry over the intent into Russian.
 * Also, in the manga, one can destroy the body and still make off with the Star Seed. This makes for some rather unsettling images.
 * In Inuyasha, "soul" can refer to the power to animate the body (Life Energy) or your true consciousness (what most would call a soul, but fits Mind better on this page.) Until the time it was explained, the word had been used interchangeably for either. (This makes Kikyo look like much less of a dick than she did when it seemed that she was condemning innocent young women to eternal oblivion to keep herself going.)
 * Kagihime Monogatari has "stories" inside of people. From the way these operate, they mostly contain aspects of memory, though there seems to be a slight overlap with soul in them.
 * Shugo Chara has eggs inside of people, their "would-be selves", that appear to be some form of dreams. They overlap with this and Ghost in the Machine, as not only do they give a person their ambition, they also take the form of little people.
 * Hayate the Combat Butler's Saginomiya family uses the blood of others as they're close to dying (essentially their Life Energy) to keep their powers. Ginka, Isumi's great grandmother uses it to maintain her youth. Isumi uses it to restore her powers. Hayate is the subject of both, and Ginka's attempt leaves him shrived for a while. Isumi just sips from the blood from a head injury, so there's no real effect on him.
 * In Fullmetal Alchemist they utilize Mind, Body, Soul, Life Energy, and the addition of Truth. Body and soul are intimately bound to one another; so long as both exists, the two will instinctively seek each other out. The presence of a soul in a body other than its own will cause the body to weaken and decay. The Mind exists as a bridge between the two. The Soul is in fact a form of concentrated Life Energy which, applied properly, can utilize the individuals Gate of Truth to perform alchemy.
 * Bleach has a relatively simplistic anatomy of the soul: The Mind is part of the Soul, the Body merely being a vessel for its interactions in the living world. The soul's Heart is the seat of the human emotions, like empathy and happiness; if the heart is consumed by negative emotions, it will disappear and the Soul will devolve into a Hollow.
 * Additional anatomy is associated with the soul but never fully detailed. The soul rest and soul chain are two vital components of the soul that control the generation of its power; Arrancar also possess them due to their transformation to be more like a Shinigami.
 * The Heart was eventually revealed to not fully disappear when a Hollow is born. Rather, it is distorted by the negative feelings into forming the Hollow's mask and acts as the source of its powers.
 * The Bounts are an example of mutant souls created by a Soul Society experiment.
 * Neon Genesis Evangelion shows all living beings to have only one important element: The Soul. The Soul in turn generates an Anti-Terror Field to keep itself distinct from the world and maintains the physical body's form. Destruction or extraction of the Soul reduces the body to LCL.
 * NGE's souls are actually more along the lines of the Freudian Ego, with the AT fields filling in as the ego barriors. That's why Instrumentality can happen. The plan is to eliminate lonelyness by collapsing the ego barriors of all living things into one unified being.
 * Angels are notable in that their Soul assumes the physical form of a red sphere, deemed the "Core" by NERV.
 * Kaoru dubbed the Absolute Terror Field to be "the light of our souls".
 * Interestingly, Shinji and Warhammer 40 K had a slightly different take on it called "Absolute Territory Field" and explained it as sort of a region where the quantum observations of a consciousness collapsed wave functions in to certain states, therefore causing consciousness to actually change reality somewhat.
 * It is called "Absolute Territory Field" in the original series as well, at least in the Japanese version. Why it is translated into "Absolute Terror Field" is probably just a mistake by the producers.
 * Soul Eater breaks it down into body, mind and soul, stating as one of its oft-repeated (moreso early on) phrases that "a healthy soul lives in a healthy mind and healthy body"; the implication being that the state of one affects the rest. The progress or lack thereof of all characters can to an extent be brought back to their state in relation to this concept. It's simplistic and neat in theory, though in practice gets some odd applications - Crona in particular.
 * In Shaman King, soul is divided into spirit, mind/will, and heart as three major components. That is not to say body doesn't have a role too, but it's not as important as the other three (being a physical component instead of a spiritual one).

Literature

 * Philip Pullman's His Dark Materials has a clear distinction of Mind, Body and Soul. The body is self-explanatory. The soul, in some worlds, lives outside of the human host as an animal-shaped dæmon. As a child, the dæmon's shape changes with moods and thoughts, but around puberty, a person's dæmon "settles" into one shape, that reflects the mature temperament and character of its owner. The mind is self-explanatory, and is the only part of the three that "survives" death as a ghost, but a ghost can also fade away into nothing. Pullman has said that the dæmon is "the part of a human that leads us towards wisdom."
 * Of course then people apparently also have a 'death' as well, that is, a conscious entity that eventually leads you to the land of the dead. What makes it odd is that it is implyed they are something very similar to daemons...
 * In The Dresden Files, minds can be manipulated by psychomancy, and souls can be manipulated by necromancy -- both are considered Black Magic. The soul is known to be necessary for life, and can be seen through a "soulgaze" by wizards; it also seems to be tied to free will. Exactly how it interacts with the mind isn't yet clear, though. Later in the series, Harry is granted the ability to use "Soulfire" to augment his magic, and it is described as being fueled directly by his soul (Bob assures him that the part of his soul thus consumed will effectively "grow back.")
 * Ghosts aren't souls, but imprints left by powerful emotions of a dead person, a fact which Harry uses to his advantage in Grave Peril; Ghost Story further establishes that all of the powers ghosts can display are fueled by memory, since that is more or less all they are composed of. Ghost Story also demonstrates that it is possible for an actual soul to exist in a state almost identical to that of being a ghost, under special circumstances.
 * There's also Life Energy, which is a source of power for magic, and a wizard's Death Curse is powered by all his life energy (therefore killing him).
 * In Stone of Tears, it is stated that Devil's ultimate punishment (reserved for everyone should he enter the world of living) is eternal existence as a mind separated from soul.

Live Action TV

 * Angel had an episode where a Las Vegas casino owner stole the destiny of important guests and sold them on the black market. Anyone who lost their destiny would have literally "nothing" happen to them-- without a destiny, they were incapable of affecting or being affected by worldly events. Eventually, the plot was foiled thanks to some celestial intervention helping a de-destinied Angel win at a slot machine, or have "something" happen.
 * My Name Is Earl revolves around the main character's attempts to level his Karma by atoning for all the bad deeds in his life.

Religion and Mythology

 * Chinese philosophies divided the soul into Hun and Po (Japanese: Kon and Paku). To put it simply, the Hun is the "ethereal" soul that leaves the body after death and reincarnates, while Po is the "corporeal" soul that resides in the body after death for some time before returning to Earth. The number isn't equal; there are 3 Hun and 7 Po. There is also Qi, the Life Energy.
 * Older Than Dirt: Ancient Egyptian beliefs involved a six-part individual, with something different happening to each part after death. All six parts had to be intact for a person to enjoy an afterlife.
 * The Ib, which was the heart and worked like this trope's Heart, containing a person's mind, memories, and personality.
 * The Shut, or shadow. It didn't do anything of major significance, but the ancient Egyptians believed that a person couldn't exist without a shadow and a shadow couldn't exist without a person, so it stuck with them even after they died.
 * The Ren, or name. The Egyptians believed that this part of a person would live as long as their name was spoken and remembered. Conversely, if the name was erased from all written and living memory, that person would cease to exist and have no afterlife.
 * The Ka (Life Energy), which met up with the ba in the afterlife. A person died when it left the body. It was sustained by food and drink, which was why the Egyptians left offerings of food and beer to the dead.
 * The Ba, the spiritual force of an individual. In the afterlife it reunited or combined with the ka to form the Akh.
 * The Body was known as the Ha, and its preservation was essential for the afterlife, leading to the practice of mummification.
 * The Aztecs separated the soul into three components. The first was the heart, or yollotl, the soul of the body. The second was the spark of life, or tonal, the spiritual soul. The third was a spiritual animal totem or nagual, the shadow soul.

Tabletop Games

 * The tabletop RPG Exalted --inspired by Chinese mythologies, amongst other things-- uses Body, Essence (fundamental building block of what you are), and Soul (divided into two parts; the Hun, or higher soul-which is the seat of reason and rational thought and is also what ordinary ghosts come from...and the Po, or lower soul-the seat of passion, destructive impulses, and instinct. Wild hungry ghosts can come from the Po, and it's also where a Celestial Exalt's shard of Exaltation resides).
 * That's nothing compared to the Primordials/Yozis. Every Primordial possesses a number of souls (somewhere between less than ten to several dozen) which each act as a seperate self-willed being that personifies a quality of the Primordial's personality or an expression of its defining theme, with a particular one (called the fetich) being the heart of the Primordial's nature. In turn, each of these souls will have a collection of external souls of their own, who serve a similar (although more stringently defined) function. Those souls are capable (though not required) of creating further souls (who are always lesser creatures and the very bottom of the hierarchy, with little standards as to their nature or purpose). The death of a second-circle soul can cause minor, cosmetic changes to a Primordial (which can be reversable), while the death of a third-circle soul causes major changes to it (often losing or warping the quality associated with the soul in question), and fetich death completely redefines the nature or personality of the Primordial. Presiding over this hierarchy are the jouten of the Primordial; its actual body/bodies, which houses its core consciousness and its powers.
 * On the other hand, The Fair Folk are much simpler on a spiritual level. At their core is the "Heart" grace, which contains their overall essence and self. Around it they build the four primary graces of Cup, Wand, Sword, and Coin, from which they derive both their powers, and their ability to relate with others. They then have feeding mouths, one for commoners and two for nobles, which are used to consume emotions from other creatures. Of course it's not an actual soul, but rather an artificially constructed imitation of one, being creatures of pure chaos posing as individuals.
 * Mummy: The Resurrection has the soul divided into Ka (roughly, Avatar), Ba (Mind), Sahu (Light), Khu (Dreams), and Sehut (or something, I forget what term was used) (Darkness). They also threw in Ren (True Name) and Sekhem (Life Energy).
 * Warhammer Fantasy Battle sourcebooks first divided the soul into anima and animus (similar to the Exalted example)) and later declared that it comprises seven different parts (see the egyptian system below) as a means of classifying the varieties of Undead.
 * Most RPGS where death is common and reversible (such as Dungeons and Dragons) have a soul, a body, and a mind -- the mind can be subject to magical or psychic events, the body is subject to physical events, and the soul is usually ignored until death, when it separates from the body and needs to be retrieved if the character is to be resurrected. Any magic that fools around with souls, such as necromancy, is usually considered evil.
 * Scion uses the Egyptian mythology variant with the Pesedjet (Egyptian pantheon) only Boon of Heku, which allows the Scion to manipulate the various parts of their soul to great effect.
 * Changeling: The Lost has perhaps the most unusual variation in a tabletop game. A character's shadow is a metaphor for their soul. The shadow always appears as the real body, rather than the Mask. To make a Fetch, the Fae remove a small strip of the shadow and bind it into the creation ritual. This is a metaphor for taking a bit of the soul, but to the Fae, a metaphor is as good as the real thing. Whether or not they've actually torn off a bit of your soul is up to the individual storyteller.
 * The importance of the soul in Mage: The Awakening means it gets a fair bit of attention. Besides describing what the soul is (the source of inspiration, will to live, curiosity, empathy for others, and sense of connection to the world) and the effects of its loss, the soul is also the basis of magic, and manipulation of the soul can be used to gain powers. The soul is also the basis for an individual's Mental World, which contains worlds which personify their personality, experiences, and dreams, and is inhabited by beings such as their daimon (personification of their desire for self-improvement, and personal criticism) and goetic demons (personifications of vices and flaws). Individual souls are also connected to the soul of humanity as a whole, and the earth itself.
 * Vampire: The Requiem introduced the Egyptian flavor in the Mekhet clanbook with the option of "Hollow" Embraces, wherein a person is Embraced after they're already dead. Thing is, their Ka has already been wandering around for a while, and it gets pissed off when it finds out it's going to be shackled to this plane again. Hollow vampires can't appear in reflections or on tape, and their voice doesn't carry over the phone; the Ka gets all that, and if it's not properly sated, it will use those abilities to terrorize the vampire and turn people against it.

Toys

 * Bionicle has used both light/darkness and dream examples.
 * The 2008 story involved Matoran having their Light drained out and becoming inherently evil, while Takanuva got partially drained and gained a Super-Powered Evil Side.
 * The serial Sahmad's Tale features a plague which robs the victims of their dreams, causing insanity and death.
 * Although it's later revealed that this "plague" is actually an Eldritch Abomination feeding on the victims' dreams.

Video Games

 * Kingdom Hearts has Soul, Heart, and Body. There might or might not be a Mind in there, it's unclear whether it's a fourth entity, or part of Soul or Heart. Also, it gets a bit confusing regarding Nobodies and Heartless, because both are misnomers. Heartless are Hearts that are consumed by Darkness, without the Body and Soul, Nobodies are Body and Soul leftover from said consumed Hearts. Unversed are born from negative emotions, specifically
 * The names do not describe their physical makeup. Heartless are called as such because of their lack of empathy or morality ("You're heartless!!!), Nobodies are called because they don't exist ("Nobody is in the room")
 * Just to complicate things further, the more recent games increase the prominence of Memory as part of the soul's anatomy. Replicas (Creatures made of pure memory) and Sentiments (imprints left behind when someone is ) have appeared in the most recent games. Word of God says that
 * Marluxia has also said that the complete loss of memory will destroy the heart.
 * Just a note, it seems like only the Pureblood variety of Heartless actually generate more Heartless when they take the heart away. The Emblem variety seem to store the heart somehow. (As evidenced by the fact that killing an Emblem causes it to release hearts and killing a Pureblood does not.)
 * A reply to the note above, and a bit of WMG: Purebloods are formed when the heart is naturally taken over by its own darkness, which then causes said heart to collapse. Emblems, on the other hand, are from darkness forcibly given form from within the heart. Since the heart didn't collapse under darkness naturally, it only makes sense that they still keep an intact heart.
 * In Saga Frontier
 * Persona uses a kind of Jungian Soul Anatomy, though it tends to focus primarily on the Mind. A Persona is a physical manifestation of the wielder's psyche. In the original, one character's consciousness is split in three, an "Ideal" version, an "Innocent" version, and a Malevolent "Id" version. In Persona 4, a character's repressed feelings manifest themselves as a Shadow, which can become a Persona when accepted. Igor does say that the power of Persona is the power to control one's Heart, which is why Social Links are so important in the later games. (When a character's without the Wild Card has a strong enough bond with the protagonist, their Persona literally evolves.) Dreams also extremely important in each game. (Igor or Philemon usually first contacts the protagonists through a dream.) Finally, Destiny plays a major role in each of the games. In Persona 3 and 4, it's explicitly stated that only those bound by a "contract" (the contract in P3 reads "I chooseth this fate of my own free will,") may enter the Velvet Room. Both Persona 2: Innocent Sin and Persona 2: Eternal Punishment has Shadows similar to the kind found in P4, though they don't seem to have the same relation to Personas. Innocent Sin, meanwhile, also has Shadow Selves, who have lost their dreams.
 * The separation of the Persona 2 Shadows needs some clarification. While they are born of essentially the same process as P4 Shadows, it was triggered by Nyarlathotep- certainly nothing you'd ever want mucking with the dregs of your soul.
 * Shin Megami Tensei Nocturne states the emotional energy (life energy) of humans, called Magatsuhi, is a massive energy source. Draining is extremely painful and leaves the victim weak and despondent. Controllers of this substance can command anything up to gods, spirits and demons, and enough of it (AKA all of Humanity), judiciously used, can be used to destroy and rebuild reality in the image of the user desires.
 * Disgaea 3 Absence of Justice has the "Heart Vault" where one can lock away or (more difficult) unlock aspects of the personality. Ah...be careful, as any changes or things killed will have radically effects on the owner..
 * In Pokémon Platinum, the Lake Trio brought about and seem to represent the makeup of soul. Uxie, the being of Knowledge, has elements of Mind, While Azelf and Mesprit, the beings of Will and Emotion, hold Dreams and Heart, respectively.
 * In Tales of Symphonia, the Heart and sometimes Mind portions of a person's soul can be The entire soul can also potentially survive outside a person's body through use of, and indeed this fact is key to understanding the motives of the Big Bad -  It's not a pleasant existence, though.
 * Also, Dragon Age: Origins, has a little of this. When you dream, your soul goes wandering in a parallel dimension called the Fade. The Fade has somewhat amorphous properties, but lots of demons and spirits linger here. They're very interested in mages, who can enter the Fade completely conscious and aware of what's happening; unfortunately for the mages, only the nastiest of demons seem to take interest... mostly.
 * Touhou occasionally delves into the matter of the soul. Hourai immortals drank elixir that caused them to separate their soul from their body, and their soul then able to generate physical body on their own that aren't subject to aging and will regenerate if damaged. On the other hand, Youmu Konpaku (whose family name is taken from the concept of Hun and Po in Chinese mythologies) is a half-ghost, part of her soul (Fan Nickname'd Myon) is outside her body.

Western Animation

 * One of Teen Titans' early episodes involves Beast Boy and Cyborg falling into Raven's mind and the three having to battle with one of Raven's many emotions. Later on in the Teen Titans Go! comics, Raven ends up having all her emotions escape her mind, only for the group to have to recapture them again. A later issue has it turning out that they missed one (Of course, Rage), and though Raven is happy with this, since it's the first time in a while where she's been able to really feel emotions without worrying about things taking a turn for the worse, she realizes that she needs to have all her emotions and takes Rage back into her mind.

Real Life

 * Plato divided the soul into the Reason, the Passions (courage and the like), and the Appetites (the Lowest Common Denominator drives, the "four F's" if you will).
 * Later elaborations of Aristotelian philosophy distinguished between Corpus (body/matter,) Animus (animal life energy) and Spiritus (consciousness/soul.)
 * Sigmund Freud's theory of the consciousness is arguably a version of Plato's tripartiate soul, with the Id being the Appetites, Ego being the Passions and Superego being Reason.
 * Timothy Leary divided the Mind into 8 "circuits". Later, he decided that this was inaccurate, and divided each of the 8 circuits in 3, for a total of 24 components of the mind. His occasional co-writer Robert Anton Wilson pointed out that this too was incomplete...
 * In a literal example of Soul Anatomy, the sacrum (a bone in the pelvis) was named that because it was once held to be sacred as the "seat of the soul", or at least its generative component. The sacrum is usually the last part to fall to pieces when a human body decomposes, and it was thought in medieval times that the resurrected dead would regenerate their bodies from this bone on Judgement Day.