Supernumerary body parts are most commonly a congenital disorder

Congenital disorder

A congenital disorder, or congenital disease, is a condition existing at birth and often before birth, or that develops during the first month of life , regardless of causation...

 involving the growth of an additional part of the body

Body

With regard to living things, a body is the physical body of an individual. "Body" often is used in connection with appearance, health issues and death...

 and a deviation from the body plan

Body plan

A body plan is the blueprint for the way the body of an organism is laid out. An organism's symmetry, its number of body segments and number of limbs are all aspects of its body plan...

. Body parts may be easily visible or hidden away, such as internal organ

Organ (anatomy)

In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...

s.

Many additional body parts form by the same process as conjoined twins

Conjoined twins

Conjoined twins are identical twins whose bodies are joined in utero. A rare phenomenon, the occurrence is estimated to range from 1 in 50,000 births to 1 in 100,000 births, with a somewhat higher incidence in Southwest Asia and Africa. Approximately half are stillborn, and a smaller fraction of...

: the zygote

Zygote

A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...

 begins to split but fails to completely separate. This condition may also be a symptom of repeated occurrences of continuous inbreeding

Inbreeding

Inbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...

 in a genetic line.

It has been suggested that deliberately adding supernumerary limbs to humans may be possible, as a form of body modification

Body modification

Body modification is the deliberate altering of the human body for any non-medical reason, such as aesthetics, sexual enhancement, a rite of passage, religious reasons, to display group membership or affiliation, to create body art, shock value, or self expression...

.

Specific types of occurrence

Specific types of additional body parts include:

• Accessory breast
  Accessory breast
  Accessory breasts, also known as polymastia, supernumerary breasts, or mammae erraticae, is the condition of having an additional breast...
  
   – one or more additional breast
  Breast
  The breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues...
  
  s
• Cervical rib
  Cervical rib
  A cervical rib is a supernumerary rib which arises from the seventh cervical vertebra. It is a congenital abnormality located above the normal first rib. A cervical rib is present in only about 1 in 500 of people; in even rarer cases, an individual may have two cervical ribs...
  
   – an additional rib
  Rib
  In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...
  
  
• Diphallia
  Diphallia
  Diphallia, penile duplication , diphallic terata, or diphallasparatus, is a medical condition in which a male infant is born with two penises. This is an extremely rare disorder with only approximately 100 cases of diphallia recorded since the first, reported by Johannes Jacob Wecker in 1609...
  
   - Having two penes/penises
  Penis
  The penis is a biological feature of male animals including both vertebrates and invertebrates...
  
  .
• Hermaphroditism
  Hermaphrodite
  In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
  
   – having both sexes' sex organ
  Sex organ
  A sex organ, or primary sexual characteristic, as narrowly defined, is any of the anatomical parts of the body which are involved in sexual reproduction and constitute the reproductive system in a complex organism; flowers are the reproductive organs of flowering plants, cones are the reproductive...
  
  s
• Hyperdontia
  Hyperdontia
  Hyperdontia is the condition of having supernumerary teeth, or teeth which appear in addition to the regular number of teeth.-Types:Supernumerary teeth can be classified by shape and by position...
  
   – additional teeth
  Tooth
  Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...
  
  
• Pelvic digit
  Pelvic digit
  A pelvic digit, pelvic finger, or pelvic rib is a rare congenital abnormality in humans, in which bone tissue develops in the soft tissue near the pelvis, resembling a rib or finger and often divided into one or more segments with pseudo-articulations. Pelvic digits are typically benign and...
  
   – a bony growth in the soft tissue of the pelvic region
• Polycephaly
  Polycephaly
  Polycephaly is a condition of having more than one head. The term is derived from the Greek stems poly- meaning 'much' and kephali- meaning "head", and encompasses bicephaly and dicephaly . A variation is an animal born with two faces on a single head, a condition known as diprosopus...
  
   – an extra head
  Head
  In anatomy, the head of an animal is the rostral part that usually comprises the brain, eyes, ears, nose and mouth . Some very simple animals may not have a head, but many bilaterally symmetric forms do....
  
  
• Polydactyly
  Polydactyly
  Polydactyly or polydactylism , also known as hyperdactyly, is a congenital physical anomaly in humans, dogs, and cats having supernumerary fingers or toes....
  
   – additional finger
  Finger
  A finger is a limb of the human body and a type of digit, an organ of manipulation and sensation found in the hands of humans and other primates....
  
  s or toe
  Toe
  Toes are the digits of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being digitigrade. Humans, and other animals that walk on the soles of their feet, are described as being plantigrade; unguligrade animals are those that walk on hooves at the tips of...
  
  s
• Polymelia
  Polymelia
  Polymelia is a birth defect involving limbs , in which the affected individual has more than the usual number of limbs. In humans and most land-dwelling animals, this means having five or more limbs...
  
   — an extra arm or leg.
• Polyorchidism
  Polyorchidism
  Polyorchidism is the incidence of more than two testes. It is a very rare congenital disorder, with fewer than 100 cases reported in medical literature. The most common form is triorchidism, or tritestes, where three testes are present. The condition is usually asymptomatic...
  
   – having three or more testicle
  Testicle
  The testicle is the male gonad in animals. Like the ovaries to which they are homologous, testes are components of both the reproductive system and the endocrine system...
  
  s
• Supernumerary kidney
  Supernumerary kidney
  A supernumerary kidney is an additional kidney to the number usually present in an organism. This often develops as the result of splitting of the nephrogenic blastema, or from separate metanephric blastemas into which partially or completely reduplicated ureteral stalks enter to form separate...
  
   – a third kidney
  Kidney
  The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
  
  
• Supernumerary nipple
  Supernumerary nipple
  A supernumerary nipple is an additional nipple occurring in mammals, including humans...
  
  s – an additional nipple
  Nipple
  In its most general form, a nipple is a structure from which a fluid emanates. More specifically, it is the projection on the breasts or udder of a mammal by which breast milk is delivered to a mother's young. In this sense, it is often called a teat, especially when referring to non-humans, and...
  
  
• Supernumerary Phantom Limb
  Supernumerary phantom limb
  Supernumerary phantom limb refers to a condition where the affected individual believes and receives sensory information from limbs of the body that do not actually exist, and never have existed, on the contrary to phantom limbs, which appear after an individual has had a limb removed from the body...
  
  s – where the brain acts as though a limb is there, but it is not.
• Syndactyly
  Syndactyly
  Syndactyly is a condition wherein two or more digits are fused together. It occurs normally in some mammals, such as the siamang and kangaroo, but is an unusual condition in humans.-Classification:...
  
   – webbing between the fingers or toes
• Uterus didelphys – (also Uterine Septum) have two vaginal canals and/or uteri
• Supernumerary bone in the feet – these additional bones are fairly common. They tend to occur between the metatarsal and are frequently mistaken for fractures on x-rays.

Related conditions and concepts

Vestigial structures are anatomical

Anatomy

Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...

 structures of organism

Organism

In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

s in a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 which are considered to have lost much or all of their original function through evolution

Evolution

Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

. These body parts can be classed as additional to the required functioning of the body. In human anatomy

Human anatomy

Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...

 the vermiform appendix

Vermiform appendix

The appendix is a blind-ended tube connected to the cecum , from which it develops embryologically. The cecum is a pouchlike structure of the colon...

 is sometimes classed as a vestigial remnant.

Prosthesis

Prosthesis

In medicine, a prosthesis, prosthetic, or prosthetic limb is an artificial device extension that replaces a missing body part. It is part of the field of biomechatronics, the science of using mechanical devices with human muscle, skeleton, and nervous systems to assist or enhance motor control...

 is an artificial extension that replaces a body part, and cybernetics

Cybernetics

Cybernetics is the interdisciplinary study of the structure of regulatory systems. Cybernetics is closely related to information theory, control theory and systems theory, at least in its first-order form...

 is the study of computer technology in relation to organisms which can include replacement or additional body parts.

Body integrity identity disorder

Body integrity identity disorder

Body Integrity Identity Disorder , formerly known as Amputee Identity Disorder, is a psychological disorder wherein sufferers feel they would be happier living as an amputee...

 (BIID) is a psychiatric disorder

Psychiatry

Psychiatry is the medical specialty devoted to the study and treatment of mental disorders. These mental disorders include various affective, behavioural, cognitive and perceptual abnormalities...

 in which a person thinks that they have one or more additional limb

Limb (anatomy)

A limb is a jointed, or prehensile , appendage of the human or other animal body....

s than they should, despite having two arms and two legs. People with this condition often wish to amputate what they see as additional body parts.

A phantom limb

Phantom limb

A phantom limb is the sensation that an amputated or missing limb is still attached to the body and is moving appropriately with other body parts. 2 out of 3 combat veterans report this feeling. Approximately 60 to 80% of individuals with an amputation experience phantom sensations in their...

 is the sensation that a missing limb is still attached to the body.

A Supernumerary Phantom Limb

Supernumerary phantom limb

Supernumerary phantom limb refers to a condition where the affected individual believes and receives sensory information from limbs of the body that do not actually exist, and never have existed, on the contrary to phantom limbs, which appear after an individual has had a limb removed from the body...

 is the sensation of having an extra limb or body part despite no such limb actually existing. It is an uncommon syndrome, usually due to some kind of brain injuries in the somatosensory cortex or in some parts of the right hemisphere of the brain, usually due to a stroke

Stroke

A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

 in the brain.

A chimera

Chimera (genetics)

A chimera or chimaera is a single organism that is composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction. If the different cells have emerged from the same zygote, the organism is called a mosaic...

  is an animal

Chimera (genetics)

A chimera or chimaera is a single organism that is composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction. If the different cells have emerged from the same zygote, the organism is called a mosaic...

 or plant

Chimera (plant)

Chimeras in botany are usually single organisms composed of two genetically different types of tissue. They occur in plants, on the same general basis as with animal chimeras...

 that has two or more different populations of genetically distinct cells

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

 that originated in different zygote

Zygote

A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...

s that have merged; anatomical structures are typically mixed depending on which cells are prevalent in different body parts, for example plants can have two different types of flowers.

A mosaic

Mosaic (genetics)

In genetic medicine, a mosaic or mosaicism denotes the presence of two populations of cells with different genotypes in one individual who has developed from a single fertilized egg...

 is a genetic anomaly similar in nature and effects to a chimera: genetically different populations of cells within one organism, originated from some propagated mutation of a single cell rather than from outside sources.

Mythology

In Hindu mythology

Hindu mythology

Hindu religious literature is the large body of traditional narratives related to Hinduism, notably as contained in Sanskrit literature, such as the Sanskrit epics and the Puranas. As such, it is a subset of Nepali and Indian culture...

 additional limbs and heads are considered a sign of power.

In Greek mythology

Greek mythology

Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

, Artemis

Artemis

Artemis was one of the most widely venerated of the Ancient Greek deities. Her Roman equivalent is Diana. Some scholars believe that the name and indeed the goddess herself was originally pre-Greek. Homer refers to her as Artemis Agrotera, Potnia Theron: "Artemis of the wildland, Mistress of Animals"...

, the goddess of fertility, was sometimes represented as having numerous breasts. This was particularly notable in the cult of Artemis (Diana

Diana (mythology)

In Roman mythology, Diana was the goddess of the hunt and moon and birthing, being associated with wild animals and woodland, and having the power to talk to and control animals. She was equated with the Greek goddess Artemis, though she had an independent origin in Italy...

) celebrated in the ancient city of Ephesus

Ephesus

Ephesus was an ancient Greek city, and later a major Roman city, on the west coast of Asia Minor, near present-day Selçuk, Izmir Province, Turkey. It was one of the twelve cities of the Ionian League during the Classical Greek era...

, in modern Turkey

Turkey

Turkey , known officially as the Republic of Turkey , is a Eurasian country located in Western Asia and in East Thrace in Southeastern Europe...

.

In Japanese mythology

Japanese mythology

Japanese mythology is a system of beliefs that embraces Shinto and Buddhist traditions as well as agriculturally based folk religion. The Shinto pantheon comprises innumerable kami...

, the God of the sea and storms, Susanoo

Susanoo

, also known as is the Shinto god of the sea and storms. He is also considered to be ruler of Yomi.-Myths:In Japanese mythology, Susanoo, the powerful storm of Summer, is the brother of Amaterasu, the goddess of the sun, and of Tsukuyomi, the god of the moon. All three were born from Izanagi, when...

, is sometimes depicted as having a third arm.

In the Bible

Bible

The Bible refers to any one of the collections of the primary religious texts of Judaism and Christianity. There is no common version of the Bible, as the individual books , their contents and their order vary among denominations...

, Goliath has brothers that have six fingers and six toes.