Acephaly is a congenital disorder characterised by absence of the head. Unlike anencephaly which is characterised by the absence of a major portion of the brain, skull, and scalp, this type of cephalic disorder is even rarer. The acephalic fetus is a parasitic twin attached to an otherwise intact fetus. The acephalic fetus has a body but lacks a head and heart; the fetus's neck is attached to the normal twin. The blood circulation of the acephalic fetus is provided by the heart of the twin. The acephalic fetus cannot exist independently of the fetus to which it is attached. Similarly, acardiac fetuses lack everything from the heart upwards, including head and arms, and behave similarly to acephalic fetuses.