The first species of the Dicephalus is the Dicephalus Dibrachius—a two-armed, double-headed monster. In this species most of the viscera are single, but the right and left halves of each viscus are supplied by the respective foetuses, and the entrail does not become indistinguishably single until near the lower end of the ileum. There may be two ordinary kidneys and a third smaller one, two pancreatic glands, and two gall-bladders. Such a monster may be monauchenous or diauchenous.
The next species is the Dicephalus Tribrachius Dipus—two heads, three arms, and two legs. There is also a Dicephalus Tribrachius Tripus (three arms and three legs), D. Tetrabrachius Dipus (four arms and two legs), and D. Tetrabrachius Tripus (four arms and three legs). In all these cases there is no doubt of the presence of twins, unless there might be some doubt as to dual personality in the Dicephalus Dibrachius. In the Dicephalus Tetrabrachius Dipus and the Dicephalus Tetrabrachius Tripus there is almost complete duplication of the internal organs, and the halves of the composite body belong evidently to individuals distinct in thought, volition, and character. Each brain controls only its own half of the body. There are four lungs, two hearts (sometimes in one pericardium), two stomachs, two intestinal canals down to the colon or lower, two livers (sometimes joined), four kidneys (or three, one of which is small), two bladders, emptied at different times through a common urethra.
Dicephali are somewhat common. Förster found 140 among 500 specimens of monsters. They are rarely born alive. The best known cases of dicephali that lived for any length of time are:
1. Peter and Paul, of Florence, born in 1316, lived thirty days.
2. The Scotch Brothers, born in 1490, lived twenty-eight years. They were at the court of James III. Above the point of union the twins were independent in sensation and action, but below the point all sensation and action were [{81}] common. One died before the other, and the second "succumbed to infection from putrefaction" a few days later.
3. The Würtemberg Sisters, born in 1498.
4. The twins, Justina and Dorothea, born in 1627, lived six weeks.
5. Boy twins at Padua, born in 1691, lived to be baptised.
6. Rita-Cristina, born at Sassari in Sardinia in 1829. They lived eight months. These children had a common trunk below the breast, one pelvis, and one pair of legs. Rita was feeble and quiet, Cristina vigorous and lively. They suckled at different times; and sensation in the heads and arms was individual, but below the junction it was common. Rita died of bronchitis, and during Rita's final illness Cristina was healthy; but when Rita died, Cristina, who was suckling at the time, suddenly expired. They had two hearts in one pericardium, the digestive tracts did not fuse until the lowest third of the ileum was reached. The livers were fused, the vertebral columns were distinct throughout. These twins were baptised separately.
7. Marie-Rose Drouin, born in Montreal in 1878. They lived seven months. Marie died of cholera infantum; and Rose then died, although she had not been directly affected by the disease. These twins were like Rita-Cristina anatomically except that they had no legs. The respirations and heart-pulsations differed, and one child slept while the other child cried.