1. The Gemara discusses how much of a fetus must be missing in order for it not to be considered a Halachic birth.
2. The above (#1) discussion applies only to the development of the fetus from the bottom up.
3. There is a dispute about a fetus that has two backs and two spines.
4. A woman who gives birth to a demon has had a Halachic birth.
5. Aba Shaul discussed what he learned by being involved in burials.
A BIT MORE
1. Rebbi Zakai: If the body of the fetus begins only above the knees and is missing everything below the knees, it is not a Halachic birth. Rebbi Yanai: If the body starts above the areas that emit waste, it is not a Halachic birth. Rebbi Yochanan: If the body starts above the navel, it is not a Halachic birth.
2. In contrast, if it is missing even just part of the top of its head, it is not considered a Halachic birth.
3. Rav: Such a fetus is not considered a Halachic birth. Such a fetus born from a Kosher animal is forbidden to eat. Shmuel: It is considered a Halachic birth, and when born from a Kosher animal it is permitted to eat.
4. Rebbi Yosi: It is a regular child that developed wings (demons have human form and wings).
5. He noticed that people who drank undiluted wine had burned bones, those who drank heavily-diluted wine had black bones or bones with little marrow, and those who drank normally-diluted wine had healthy bones.