The chief single forms of deviation are divided as follows:

1. Aplasia, or complete failure of development, which may be either general or local. If general, abortion usually results and the embryo is cast off. It may, however, be infiltrated with lime salts, forming a lithopedion. Examples of the local form are absence of parts of the body, as fingers, toes, and internal organs. This condition may prevent life, as in the absence of the brain or heart.

2. Hypoplasia is the failure of parts of the body to reach their full development, as in small size of limbs or of the brain. It is seen in cases where one kidney may be very large and the other very small.

3. Incomplete union along the line of closure of the fetal arches may be anterior, posterior, or lateral, such as extrusion of viscera, spina bifida, and harelip.

4. There may be an abnormal union of parts, as of the lower extremities.

5. Occasionally there is a duplication of parts, particularly of the digits; sometimes of the internal organs, as the spleen and pancreas.

6. Abnormal location of viscera. In these cases all the single organs are transposed, the heart and spleen on the right, the liver on the left side.

7. Obstruction of the external openings, mouth, anus, vagina, etc.

8. Persistent misplaced fetal structure, which may eventually give rise to neoplastic formations, usually cystic.

9. Anomalies of sex - hermaphroditism, which may be either true or false. In the early stages the embryo is bisexual, but finally one set of organs undergoes a perfect development, with slight traces only of the subsidiary organs. In the true form both sets of organs would be present, well developed. This condition is so rare that it is said not to exist, one case only having been reported.

In false hermaphroditism the malformation depends upon abnormalities of the external genitalia.