Many classifications of terata have been offered, and each possesses some advantage. The modern reader is referred to the modification of the grouping of Geoffroy-Saint-Hilaire given by Hirst and Piersol, or those of Blanc and Guinard. For convenience, we have adopted the following classification, which will include only those monsters that have LIVED AFTER BIRTH, and who have attracted general notice or attained some fame in their time, as attested by accounts in contemporary literature. CLASS 1.--Union of several fetuses. CLASS 2.--Union of two distinct fetuses by a connecting band. CLASS 3.--Union of two distinct fetuses by an osseous junction of the cranial bones. CLASS 4.--Union of two distinct fetuses in which one or more parts are eliminated by the junction. CLASS 5.--Fusion of two fetuses by a bony union of the ischii. CLASS 6.--Fusion of two fetuses below the umbilicus into a common lower extremity. CLASS 7.--Bicephalic monsters. CLASS 8.--Parasitic monsters. CLASS 9.--Monsters with a single body and double lower extremities. CLASS 10.--Diphallic terata. CLASS 11.--Fetus in fetu, and dermoid cysts. CLASS 12.--Hermaphrodites. CLASS I.--Triple Monsters.--Haller and Meckel were of the opinion that no cases of triple monsters worthy of credence are on record, and since their time this has been the popular opinion. Surely none have ever lived. Licetus describes a human monster with two feet and seven heads and as many arms. Bartholinus speaks of a three-headed monster who after birth gave vent to horrible cries and expired. Borellus speaks of a three-headed dog, a veritable Cerberus. Blasius published an essay on triple monsters in 1677. Bordenave is quoted as mentioning a human monster formed of three fetuses, but his description proves clearly that it was only the union of two. Probably the best example of this anomaly that we have was described by Galvagni at Cattania in 1834. This monster had two necks, on one of which was a single head normal in dimensions. On the other neck were two heads, as seen in the accompanying illustration. Geoffroy-Saint-Hilaire mentions several cases, and Martin de Pedro publishes a description of a case in Madrid in 1879. There are also on record some cases of triple monster by inclusion which will be spoken of later. Instances in the lower animals have been seen, the three-headed sheep of Pare, already spoken of, being one.