union is by the cephalic extremity, forehead to fore head, vertex to vertex. They are normal except at the point of union. (Fig. 212.) The anterior and the posterior portions of the foetuses are in the same planes.
united also by the heads, but they look in opposite directions. (Fig. 213.) In the above two varieties, union of the foetuses may be by an extensive surface, or else by pedicle. In the first instance, the foetuses are end to end; in the second the two bodies may be more or less inclined one to the other, or even be parallel. We would add, further, that there exist transitional stages between the metopagi and the cephalopagi, where the anterior plane of one foetus is continuous with the lateral plane of the other.
Monomphalic are characterized by the union of two complete individuals at a common umbilicus. Very few ever reach adult age.
If the union is below the umbilicus, we have an ischiopage, if above the umbilicus a xyphopage, sternopage, ectopage, hemipage.
two individuals are fused together at the umbilicus face to face. The bones of the pelvis of one foetus, instead of meeting in the median line, are separated to the right and the left to join those of the other fcetns. We thus find two lateral pubic joints. The external genital organs are similarly arranged, the right of one foetus being united to the left of the other, and vice versa. In addition, other anomalies may be noted bearing on other organs, such as extrophy of the bladder, or more or less intimate union of limbs.
the union of the individuals is above the umbili cus, that is to say, begins there and extends above to include a portion of the thorax. (Fig. 216.) The fusion of the individuals is more or less deep, in certain instances only by the skin; in others the livers unite into one vast hepatic gland. There may be two hearts contained in two peri- . cardial sacs, or in one. The two diaphragms may be continuous, form ing a single septum between the abdominal and thoracic cavities.
Xyphopages are rarer than ischiopages.
the two individuals are fused, face to face, from the umbilicus to the upper portion of the thorax. They are very similar to the preceding variety. The union of the two sternums is analogous to that of the pelves in case of the isehiopage. Each sternum is divided in the mid-line, and each half with its ribs opens outwardly like the leaves of a book. There is a single thoracic cavity, two vertebral columns, two sterno-costal walls, each wall being formed by half the sternum and ribs of one fcetus, and half of the other. There is a single
pericardial sac, containing two hearts near together or united. The large vessels of the heart are anomalous, the diaphragms are united, forming a single septum with two symmetrical halves. The lungs are four in num ber, and but little altered.
This monstrosity is not rare. They die shortly after birth, owing likely enough to anomalies in the hearts and great vessels.
Ectopage.—Characterized by inequality of the thoracic walls, or rather of the two costo-sternal walls of the double thorax, one well developed, the other more or loss imperfect. The degree of atrophy of one thorax is variable. The vertebral columns are near together. The arms ing to the atrophied side are near together, sometimes fused. The mon ster may have three or more arms. It has four lungs, but the two on the atrophied side are very small. There are two hearts situated above a ragm. The liver is often single, as also the stomach. Death immediately after birth in all the known cases.
a very rare monstrosity. We find two bodies fused at thorax, with two very unequal thoracic walls, half of which belongs ,,,ch individual. There is this essential difference from the ectopage —the fusion extends even to the mouths, which form a single cavity. (Fig. 221.) In other words, the two faces and the two necks are joined anteriorly and obliquely, the upper part of the faces and skulls being distinct.
Sycephalic Fcetuses.—Here there is no longer simply junction of the two heads, but intimate fusion. These monsters have been described under the various terms, janicephalic, janiformic, and have bodies com pletely separated below the umbilicus, and fused above. There is a single head, with two faces, the one opposed to the other. " The two faces of janiform monsters are made up exactly as are the two pelves or thoraces of isehiopages and sternopages. The right half of the head of each fcetus is separated from the left half, and the two half heads are disjointed, one from the other laterally, even as the leaves of a book may be divided, the back of the book not being displaced. The right half-face of one individual corresponds to that of the other, and unites with it, and in versely, and so there are formed two faces which are lateral. Thus there exists on each side of the head a face, one half of which belongs to one individual, and the other half to the other, and which still, in size, may be scarcely beyond the normal.