The skull of a young boy from Bengal with a second imperfect skull attached to its anterior fontanelle, 1783. From the Royal College of Surgeons, London. 

DEFINITION: Craniopagus parasiticus is a medical condition in which a parasitic twin head with an undeveloped (or underdeveloped) body is attached to the head of a developed twin. [Wikipedia]

DESCRIPTION: ‘The child was a male; it was more than four years old at the time of its death, which was caused by the bite of a cobra. It was very emaciated, a fact attributed to the parents having used it as a show, always keeping it covered up, except when payment was made for its exhibition. The woman who acted as midwife was terrified at the appearance of the additional head, and tried to destroy the child by throwing it on the fire; it was rescued after one eye and ear were considerably burnt. There was no trunk to the second head; but it was surmounted by a short neck terminating in a rounded tumour, which is stated by one observer to have been quite soft at the age of two, and by another to have been quite hard and cartilaginous at the age of four. Its external ears were represented by mere folds of skin, and there was no auditory meatus. The normal face and head were not malformed. The brains were distinct, each invested in its own membranes; the dura mater of each adhered to that of the other at the point of contact. The chief supply of blood to the upper head was by a number of vessels passing from the membranes of one brain to that of the other. The movements of the features of the upper head appear to have been purely reflex, and by no means to have been controlled by the feelings or desires of the child. The movements of the eyes of the accessory head did not correspond with those of the child, and the eyelids were usually open, even during sleep.’ [Philosophical Transactions, volume 80 (1790), p. 296].