(13) Symmetrical Double Monsters
Symmetrical Double Monsters are subdivided according to the part or region of the body where the union or fusion exists -- head, thorax, umbilicus, or pelvis.
One of the simplest cases in a Janus head upon a single body, or there may be two pairs of arms, with two faces. Again, there may be one head with two necks and two complete trunks and pairs of extremities. Two distinct heads (with more or less of neck) may surmount a single trunk, broad at the shoulders but with only one pair of arms. The fusion, again, may be from the middle of the thorax downwards, giving two heads and two pairs of shouders 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 in the respective cavities, or so great as to have the viscera in common; and there is hardly even an intermediate condition between those extremes. Thus, in the Janus head there may be two brains, or only one brain.
The Siamese twins are an instance of union at the umbilical region, with the viscera distinct in every respect a slight vascular anastomosis and a common process of peritoneum; but it is more usual for union in that region to be more extensive, and to entail a single set of abdominal thoracic viscera. The pelvis is one of the commonest regions for a double monsters to be joined at, as in the head and abdomen, the junction may be slight or total.
The Hungarian sisters Helena and Judith (1701-1723) 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 other recent case of the Bohemian sisters Rosalie and Josepha.
More usually the union in the pelvic region is complete, and produces the most fantastic shapes of two trunk (each with head and arms) joining below at various angles, and with three or four lower limbs extending from the region of fusion, sometimes in a lateral direction, sometimes downwards.
A very curious kind of double monster is produced by two otherwise distinct fetuses joining at the crown of the head and keeping the axis of their bodies in a line. It is only in rare instances that double monster survive their birth, and the preserved specimens of them are mostly of foetal size.
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