Once a question was put to Hazrat Ali (A) about the inheritance of a child having two heads, two chests but only one back. Hazart Ali (A) replied :
Let him go to sleep and then call him by name his parents have given him. If one of them wakes up, take him to be only one, otherwise two and let him inherit accordingly.
(Biharul Anwar, vol. 9, p. 486; Turuq-i-Hikamiah by Ibn-iQaiyyim, p. 53; also Abu Turab vol. 2, by AllamaJazaeri).