Abigail and Brittany Hensel
Overview
Abigail "Abby" Loraine Hensel and Brittany "Britty" Lee Hensel (born March 7, 1990) are dicephalic
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...

 parapagus twins, meaning that they are 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...

 of whom each has a separate head, but whose bodies are joined. They are highly symmetric, giving the appearance of having just a single body with little variation from normal proportion. In fact, several vital organs are doubled up, each twin having a separate heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

, stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...

, spine
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...

 and spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...

.

Each twin controls her half of their body, operating one of the arms and one of the legs.
 
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