Returning to the ventral middle line, there may be defects of closure in the breast-bone (fissure of the sternum), at the navel (the last point to close in any case), and along the middle line of the abdomen generally.
Strictly speaking, a hermaphrodite is a creature containing ovaries and testes. But in all the higher vertebrates, including man, the sex is predetermined in the fer tilized ovum, and it is more than doubtful if true hermaphroditism occurs. On the other hand, in the majority of so-called hermaph rodites, there is much doubling and ambiguity in the secondary or external organs and parts of generation. Those parts which are rudimentary or obsolete in the male but highly developed in the female, and those parts which are rudimentary in the female but highly developed in the male tend in the hermaphrodite to be developed equally, and all of them badly.
The same feebleness of the formative energy which gives rise to defective closure in the middle line, and to ambiguous sex, leads also to imperfect separation of sym metrical parts. The most remarkable case of the kind is the cyclops monster. At a point corresponding to the root of the nose there is a single orbital cavity, sometimes small and with no eyeball, at other times of the usual size and containing an eye ball more or less complete. In still other cases the orbital cavity extends on each side of the middle line, and contains two eyeballs lying close together.
Another curious result of defective separation of symmetrical parts is the siren form of foetus, in which the lower limbs occur as a single tapering prolongation of the trunk like the hinder part of a dolphin, at the end of which a foot (or both feet) may or may not be visible.
Allied to these fused or unsepa rated states of the extremities is the class in which whole limbs are absent, or represented only by stumps. The trunk (and head)
may be well formed, and the individual healthy ; all four extremi ties may be reduced to short stumps either wanting hands and feet, or with the latter fairly well developed ; or the legs only may be rudimentary or wanting, or the arms only, or one extremity.
It sometimes happens in a twin pregnancy that one of the embryos fails to develop a heart and complete vascular system of its own, depending for its nour ishment upon blood derived from the placenta of its well-formed twin by means of its umbilical vessels. It grows into a shapeless mass, in which all traces of the human form may be lost.
This is a developmental error associated with the retention of the right aortic arch as in birds, instead of the left as is usual in mammals. The position of all the unsymmetrical viscera is transposed. This condition need cause no inconvenience ; and it may remain undetected.
The causes of congenital anomalies are difficult to specify. There is no doubt that, in some cases, they are present in the sperm or germ of the parent ; the same anomalies recur in several children of a family, and it has been found possible, through a variation of the circumstances, to trace the influence in some cases to the father alone, and in other cases to the mother alone. The remarkable thing in this parental influence is that the malfor mation in the child may not have been manifested in the body of either parent, or in the grandparents. More often the malforma tion is acquired by the foetus in the course of development and growth, either through the mother or in itself independently.