They are not viable, and in no case have they ever given sign of life. Sub varieties are: Omocephalic, where the arrest of development is a trifle more accentuated. The thoracic limbs are lacking. Hemicephalic, where the head is still more imperfect. There is no mouth, the organs of sense are no longer distinct. A median superior mass is the only, external trace of skull.
Acephalic Fetuses.—These are distinguished from the paracephalic by the complete atrophy of the head, of which there exist only traces appre ciable anatomically. The organs of sense are not even formed. There is scarcely any projection above the trunk, which might be taken for a head. The upper extremity of the trunk is covered by a smooth skin like that of the rest of the body. The shape of the trunk is also abnormal. Its form is irregular and imperfectly symmetrical. The thoracic and abdominal viscera are badly formed or even absent. The thoracic viscera are particularly affected, the heart being lacking, or else only traces of the organ. Extra-uterine life is hence not possible. The genitourinary apparatus is relatively developed.
These monsters are likewise usually expelled after a twin pregnancy, the placenta being common to the twins. The foetuses are of the same sex, sometimes hermaphrodites. Often it is not possible to recognize the sex of the monster.
Anidic Fa3tuees.—The form of these monsters is as abnormal as possi ble without being indeterminate. It is ovoid, globular, pyriform. The
term acardiac has been applied to them, but it is defective, for, although certain of them have no heart, in the higher degrees vestiges of this organ are found. These monsters, however, have no circulatory system, prop erly so-called. The true heart is not in the monster, but in its brother, whose heart really works for both. The life of the monster ceases, hence, as soon as it is separated from its twin brother. It is a true parasite in intrauterine life, and is not viable externally.
Acardiacs then may be defined as the outcome of a twin pregnancy, where the foetuses are enclosed in a single amnion, and there is anastomo sis of the two vascular systems. Now in one foetus the blood pressure becomes exaggerated and diminished in the other. One fietus developer normally, therefore, and the other atrophies. The stasis in the umbilical vein causes edema and hypertrophy of the subcutaneous cellular tissue.
Spiegelberg and A hlfeld describe four varieties of acardiacs: 1. Aniorphi or mylacephali. —Spheroidal, covered with skin, Without head or extremi ties. Inside the mass are found a few rudimentary vertebrae, muscles, rudiments of the intestine. 2. Aco, nu. —Badly-shaped head, and very rudimentary trunk. The cord is attached at the neck. 3. Acephali.— There exists no head. 4. Acardtaci anceps.— The head, body, pelt, limbs, exist, as well as the heart, but these organs are atrophied.