DOUBLE MONSTERS Twins are the physiological analogy of double monsters, and some of the latter have come very near to being two separate individuals. The Siamese twins, who died in 1874 at the age of sixty, were joined only by a thick fleshy ligament from the lower end of the breast-bone (xiphoid cartilage), having the common navel on its lower border; the anatomical examination showed, however, that a process of peritoneum extended through the liga ment from one abdominal cavity to the other, and that the blood vessels of the two livers were in free communication across the same bridge. From double monstrosity, like the Siamese twins, there are all grades of fantastic fusion of two individuals into one down to the condition of a small body or fragment parasitic upon a well-grown inf ant—the condition known as foetus in foetu. These monstrosities may be deviations from the usual kind of twin gestation (one foetus being partially included within the body of the other) or from a rarer physiological type of dual develop ment. In by far the majority of cases twins have separate uterine appendages, and have probably been developed from distinct ova ; but in a small proportion of (recorded) cases there is evidence, in the placental and enclosing structures, that the twins had been developed from two rudiments which arise side by side on a single blastoderm. The perfect physiological type of this appears to be two rudiments on one blastoderm, whose entirely separate development produces twins (under their rarer circumstances), whose nearly separate development produces such double monsters as the Siamese twins, and whose less separate development produces the various forms of two individuals in one body.
be from the middle of the thorax downwards, giving two heads and two pairs of shoulders and arms, but only one trunk and one pair of legs. In another variety, the body may be double down to the waist, but the pelvis and lower limbs single. The degree of union in the region of the head, abdomen or pelvis may be so slight as to permit of two distinct organs or sets of organs in the respective cavities, or so great as to have the viscera in common ; and there is hardly ever an intermediate condition between those extremes. Thus, in the Janus head there may be two brains, or only one brain. The pelvis is one of the commonest regions for double monsters to be joined at, and, as in the head and abdomen, the junction may be slight or total. The Hungarian sisters Helena and Judith (1701-23) were joined at the sacrum, but had the pelvic cavity and pelvic organs separate; the same condition obtained in the South Carolina negresses Millie and Christina, known as the "two-headed nightingale," and in the Bohemian sisters Rosalie and Josepha.