An early biomedical treatment for mental illness called involved primitive surgery on the brain, presumably as a treatment to allow evil spirits to leave the body.

Trephining

Primitive surgery on the brain is called trephining, where hole is drill into human skull exposing the dura mater to treat mental illness related to intracranial diseases and to release pressured blood build-up from a head injury. In ancient times, burr hole was created to allow evil spirits to leave the body of a person who was behaving abnormally and the bone from the trepanned was worn to keep evil spirits away.

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.

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