Todayโs path rounds are on conjoined twins! I know how much you guys love weird developmental abnormalitiesย 
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
๐๐จ๐ง๐ฃ๐จ๐ข๐ง๐๐ ๐ญ๐ฐ๐ข๐ง๐ฌ are exactly as described: twins that are fused together at some point on their body. They have been reported throughout history, with cases even documented in medieval paintings!
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
Any species can get this!
๐๐ก๐๐ญ ๐๐๐ฎ๐ฌ๐๐ฌ ๐ข๐ญ?
The exact cause of conjoined twins is unknown, but there are two main theories: ๐๐ฎ๐ฌ๐ข๐จ๐ง and ๐๐ข๐ฌ๐ฌ๐ข๐จ๐ง. The โfusionโ theory seems to be the most convincing at this time, suggesting that two embryos become attached to each other and fuse, producing the conjoined twin. The alternative theory of fission suggests that one embryo may partially divide into two, however this theory does not seem to hold up to rigorous scientific examination.
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ ๐ฉ๐ซ๐จ๐๐ฅ๐๐ฆ?
Depending on where the twins are fused, various issues can arise. Usually the main issue in animals is locomotion, since many of these animals may have too many limbs or unusually positioned body parts to move around appropriately. Sometimes, the attachment that occurs between the twins may cause secondary issues, as it is not properly formed. For example, in ๐๐ข๐๐๐ฉ๐ก๐๐ฅ๐ข๐ ๐ฉ๐๐ซ๐๐ฉ๐๐ ๐ฎ๐ฌ conjoined twins, which have two heads on one body, one of the heads may have a poor attachment to the shared digestive and respiratory system. This may lead to ๐๐ฌ๐ฉ๐ข๐ซ๐๐ญ๐ข๐จ๐ง ๐ฉ๐ง๐๐ฎ๐ฆ๐จ๐ง๐ข๐, if food enters the airways.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
These are pretty easy to diagnose, just by looking at the animal!
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐?
Unfortunately in our animal species, treatment options are generally not feasible. In humans, there are now many surgical options available to separate the twins, depending on where they are attached!
๐๐ก๐จ๐ญ๐จ๐ฌ
1-2) Examples of dicephalic parapagus twins with two heads!
3) The brains of a dicephalic twin showing their common connection to the spinal cord.
4-7) Other examples of conjoined twins!
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Spencer R. Theoretical and Analytical Embryology of Conjoined Twins: Part I: Embryogenesis. Clinical Anatomy 13:36-53 (2000).
Photos 1-4 ยฉ Noahโs Arkive contributors King, Luginbuhl, Larsen, Beasley licensed under CC BY-SA 4.0.
Photos 5-6 ยฉ Wikimedia Commons contributor Bj.schoenmakers, Jordi ramis licensed under CC Share Alike 4.0 International.
Photo 7 ยฉ Wikimedia Commons contributor Sailko licensed under CC 3.0 Unported.
