[8] Total craniopagus twins share a large portion of dural venous sinuses and present with pronounced brain compression, leading to distortion within the cranium.

Stone and Goodrich also defined two main subtypes, based on whether the long-axis angle between the twins was angular or vertical.

[7] Stone and Goodrich define partial craniopagus twins as lacking substantial shared dural venous sinuses, with limited surface area involvement, with either intact crania or cranial defects.

The junctional diameter is often smaller in partial forms and occasionally an incomplete layer of bone may be present between the twins.

Some theorists suggested that conjoined twins develop as a result of the failed division (fission) of a single fertilized ovum.

This can happen because the cranial neuropore is still open, which is responsible for the ultimate fusion and formation of the brain stem and central nervous system.

In part because treatment of conjoined twins varies largely, many parents make the decision to terminate pregnancy due to the prognosis and quality-of -life issues.

The doctors also must consider the possibility of reconstructive surgery and the social and learning issues the twins may have to face after they are separated.

Physical traits like joined brain tissue, shared arteries and veins, as well as defects in the skull and dura mater complicate a separation operation.

[3] In 2011, The New York Times Magazine covered a story of two craniopagus twin girls who share a brain and seem to show all different kinds of physiological and emotional responses due to their condition.

[32] Although there is not an overwhelming amount of research surrounding how the union between craniopagus twins leads to different personality, cognitive and motor traits, there have been some studies exploring what it actually means to share a brain.

Studies of the thalamus' role in the brain provide neurological data that help explain these behavioral observations that these two twins experience.

The brain's ability to function through loops and circuits is a good model to explain why Tatiana consciously feels what Krista is physically experiencing.

Another study found that for craniopagus twins, their connection to each other is comparable to our normal appendages and that their bodies have obvious overlap physically and psychologically.

However, this example provides insight into the effects of a union between twins who essentially share the same sensory relay system in the thalamus.

Apart from that, Sebastian Münster’s Cosmographia universalis provides the true first account of craniopagus twins who happened to live for ten years, exceeding many expectations during that time.