In these monsters all the anomalies may be formed which have been noted under the sternopagic fetuses. There are, however, two mouths, two pharynges, one of which may end in a cul-de-sac. Each fetus has its spinal cord, and the same is true of the medulla and the cerebral hemispheres, which are not fused, the two brains often being separated by a strong septum. These monsters are born at term, and are always unisexal. The varieties are: Janiceps.—One largo head with two complete faces, or nearly so, diametrically opposed, one large thorax with two sternal surfaces, one neck larger still than the double head and thorax which it separates, one umbilicus, below which the bodies are separated, two vertebral columns. two occiputs, eight normal limbs. Rarely there have been observed the anomalies belonging to the symelic, rhinocephalic, anencephalic foetuses.
Miopes.—Where one face is normal, while the other does not really exist, but is represented by two ears very near one another, or perhaps only one median ear, and above it one orbit and an eye, more or less im perfect. Each face looks outwards, and each occiput inwards. This monstrosity is exceedingly rare.
Synotes.—The monstrosity is still more accentuated. The eye has dis appeared, and on the atrophied side only the ears are found close together or fused, often only the meatuses. This variety is relatively rare in man, but frequent in animals.
Monocephalic Retusee.—These include all the composite autosites in whom a double head without external trace of junction surmounts two bodies joined in a more or less intimate manner, and more or less exten sively. (Saint-Hilaire.) Monocephalic foetuses present two characteristics: " The first, apparent unity of the head, and secondly fusion of two bodies." (Saint-Hilaire.) When the bodies are separated below the umbilicus and united above, we have the varieties deradelphe and lhoradelphe; when the bodies are united also below the umbilicus, we have the ileadelph6 and 8ynadelphe.
These monsters are very rare in the human race. Saint-Hilaire was able to find but two instances, and not a single instance in man of thora delphic or synadelphic foetus.
the bodies are separated below the umbilicus, le united above. Four pelvic limbs, three or four thoracic limbs, a single head.
the bodies are united above the umbilicus and separated below. Four pelvic limbs and only two thoracic; one head.
lleadelphe. —One head, one neck, two thoracic limbs, one body below the umbilicus, bifurcating at the pelvis where there are four limbs.
Synade/phe.—One head, a single body including the pelvis, but there are eight limbs, four dorsal and superior.
The above figures represent varieties of preceding groups.
Sysomic are characterized by the more or less complete fusion of the two trunks, the two heads remaining distinct and separate. According to the degree of fusion, they are known as psodymes, xypho dymes, derodymes.
there is a single pelvis with two lower limbs. The lower part of the abdominal cavity is single, as also the contained viscera. Above, the trunk seems to bifurcate, so that there are two thoraces, each having two arms. The vertebral column is single below, in the lumbar region, and bifurcates at the dorsal. Sometimes a third rudimentary lower limb is seen, adherent by ligaments to the vertebral column. These monsters are very rare, and some have lived.
the fusion invades the lower part of the thoracic walls. There are two thoraces separated above, but not below. (Fig. 229.) " The vertebral columns, in certain cases at least, are entirely separate, and between them is a rudimentary pelvis usually formed of a single piece. There are two normal lower limbs. The two coxal bones are widely separated posteriorly, and between them are the sacrum and the two spinal columns. When a third rudimentary limb exists, it is attached to the centre, in front." (Saint-Hilaire.) Throughout the united thoraces exists the same mechanism as in the sternopages. A few examples of xyphodymes have been seen in the human race. They may live, and the most celebrated case is that of Ritta-Christina, on whom Serres made an autopsy. (Fig. 229.) the body is fused throughout its entire length, although there are traces externally of union. The limbs may be normal in number, although there may exist certain rudimentary buds. At the neck the body divides into two heads. (Fig. 231.) They differ only from the xyphodymes in that the vertebral columns are near together and parallel. From their external borders extend the ribs, which are inserted in front into a wide sternum, while from the internal borders extend small short ribs, which unite in the median line.
Monosomic are distinguished from those which we have studied, in that there is still more complete fusion of the bodies. There is in reality a single body surmounted by two heads. The varieties are: there are two heads on a common body, but this body has really a truly single organization. Not a single example was found by Saint-Hilaire in the human species.