( = a face), double-face (Partial duplication of head). - In this there are indications of duplication in the middle line, but the corresponding parts have coalesced more or less, so that while the head is single, the parts of the face are at least partly doubled. In the lowest degree there is apparent externally only a broadening of the head, and there is no doubling of external parts, although the mouth and nasal cavities show a certain amount of duplicity. From this there are successive degrees, the double parts emerging as it were, as successive stages are reached. As the two heads are applied laterally the eyes and nose first emerge, and then the ears. Hence, beginning with the lowest, we have cases with two eyes (Diprosopus diophthalmus), with three eyes (triophthalmus), with four eyes (tetrophthalmus), with three ears (triotus), and with four ears (tetrotus).

This form of monstrosity is rare, and as the brain and fauces are usually defective, it is not capable of life.