Miodynies. —Where the two heads are not only contiguous, but are united laterally by the occiputs. (Fig. 232.) There may be four cars or two, or even three. The neck is sometimes partially divided.
Opodymes. —Where the fusion is still more accentuated. The ocular regions are near together, and there may be two eyes in two more or less distinct orbits, two eyes in a single orbit, one orbit containing a single eye, often imperfect. (Fig. 233.) The middle parts present the anoma lies which are found in case of the Cyclops. The mouths may be near together or separated; they may even form a single cavity. Whatever the disposition of the mouths, there is always fusion of the posterior part, and while anteriorly the tongue is double, it is always single posteriorly.
In the opodymes, anencephalus or microcephalus often coexist, and usually in both heads.
Complex Parasite Monstrosities.
In the case of all the monsters we have so far studied, the two indi viduals, who by their union constitute the double monster, had about an equal volume. In those we are going to consider there is fusion of two beings, one of whom has undergone such arrest in development that it could not live independently of the other.
Heteropage.—These are characterized by the presence of a parasite suspended to the anterior abdominal wall of the principal subject. There are two distinct sets of limbs and one head. This monstrosity is very rare. (Fig. 234.) Heteradelph.—If the parasite's head is lacking, so that the body, with or without the thoracic limbs, seems to implant itself by its upper portion at the level of the epigastrium of the autosite, we call it a heteraclelpb. (Fig. 235.) It is the least rare variety in the human species.
Heterodyne.—The parasite is represented only by a more or less imper fect head implanted, by a very rudimentary neck and thorax, on the an terior surface of the autosite.
Ifeterotype.—This form, although named by Saint-Hilaire, was never described by him.
Heteromorph.—The same remark applies to this as to the preceding.
Heteratieus.—The parasite is inserted at a distance from the umbilicus of the autosite. It is constituted by a head implanted on that of the principal subject. There may be only a head, or vestiges of a trunk.
The face of the parasite is usually turned towards the right lateral plane of the antosite. The epitome, which belongs in this class, may live a number of years. Saint-Hilaire speaks of one which lived over four years. This monstrosity is very rare.
Polignathi. —These are very singular monsters. " If we imagine, at tached and as though suspended from one of the maxilize of an otherwise regular being, deformed maxillae, or even a very irregular mass of amor phous bone and cartilage, in which it is difficult to recognize the traces of a head, although the mass is covered with integument, partly cutaneous and partly mucous, then we will have an idea of the curious modifica tions which characterize a polygnathic monster." (Saint-Hilaire.) The varieties are: the parasite is inserted on the superior maxilla, usually on the palatine apophysis. (Fig.237.) the parasite is implanted on the inferior maxilla. similar to the preceding, where the head of the parasite is so imperfect, that it is really simply a rudimentary maxilla, implanted on the inferior maxilla of the autosite.
Polymelic are double monsters, where the parasite is reduced to one or two limbs, directly inserted on the autosite, and through the agency of a mass which represents the remaining part of the trunk.
Different varieties are distinguished according to the region of the auto site on which the parasite is inserted. Thus: the autosite carries in the hypogastric region one or more supplementary limbs, which are inserted behind or between the normal limbs. (Fig. 238.) Ordinarily, the accessory limbs are inserted on a pelvis the bones of which articulate with those of the pelvis of the autosite, even as the pelvic bones articulate in the pygopage. The accessory limbs are always more or less atrophied. The malformations of which they are the seat are most accentuated in the feet. If the accessory pelvis is atrophied it may close all connection with that of the autosite. In a more advanced degree the two limbs may be fused into a single.