CHAPTER VIII
EMBRYOLOGY—THE DEVELOPMENT OF LIFE
You remember I mentioned that at various times during the month an ovum or egg leaves the ovary and passes along the tube to the uterus. Here it remains if it is impregnated or fertilized by a union with the spermatozoon or male element. The whole body of the babe is developed from the ovum or female element after it has been fertilized by the spermatozoon or male element. The union usually takes place in the tube. The spermatozoon, after being deposited in the vagina, travels to the mouth of the womb, then up through the womb into one of the tubes. Here it meets the ovum and unites with it, then the impregnated ovum continues on its way to the uterus. It attaches itself to the lining of the womb by little thread-like filaments which it projects. The ovum then begins to grow, dividing itself into portions that go to make the different parts of the body. Before I continue, let me remind you that the ovum in the beginning is only about as large as the point of a pin, being about 1-125 of an inch in diameter, while the spermatozoon is so tiny it cannot be seen without the aid of a miscroscope. Therefore, it can be realized how much the ovum has to grow before it becomes a fully formed babe.
During the time the ovum is developing into the babe we speak of it first as the embryo, then the fœtus. It takes about nine calendar months or ten lunar months before the fœtus is fully developed and ready to be expelled from the womb. During the process of development the fœtus resembles various animals. It seems it must pass through about the same stages of evolution that our primitive ancestors did.
By the end of the third week, the dividing has progressed so far that the body is quite well indicated. By the end of the seventh week the body and limbs are quite well defined. One peculiar thing is that, at this time, the fœtus has a tail which disappears during the next two weeks. During the third month the fœtus increases in size and weight so that by the end of the month the weight is four ounces and the length two and three-fourths inches. It now is not directly attached to the lining of the womb but is attached by means of the cord to the placenta or afterbirth which has been forming slowly. This placenta consists of fatty tissue surrounding a great many little blood vessels. The tiny blood vessels lie so close to the blood vessels of the lining of the womb that the blood passes from one to the other. To do this, it must pass through the walls of the blood vessels, as the vessels of the mother and those of the placenta are not directly united. The blood vessels of the placenta unite to form two veins and one artery which lie very close to each other and are surrounded by a membrane. These three blood vessels united together form what we call the cord. The other end of the cord is attached to the fœtus so that the blood can flow back and forth between the fœtus and placenta.
By the end of the third month the limbs have definite shape, the nails being almost perfectly formed. During the next month the sexual distinctions of the external organs become well marked.
By the last of the fifth month the weight has increased to one pound and the length to eight inches. Active fœtal movements begin, that is, the fœtus begins to move around and not lie quietly as before. This is what is usually spoken of as "feeling life," or as "quickening." There is life from the very beginning but during the first four or five months the fœtus does not move about and so the mother does not "feel life." This has caused the erroneous idea that there is no life before the fifth month.
By the end of the sixth month the weight is two pounds and the length twelve inches. The eyebrows and eyelashes have begun to grow and the lobule of the ear is more characteristic.
By the end of the seventh month the weight is three pounds and the length fourteen inches. The surface of the body, which has appeared wrinkled, now appears more smooth owing to the increase of fat underneath.
By the end of the eighth month the weight is four to five pounds and the length twenty inches. The nails have grown to project beyond the finger tips. Up to this time the body has been covered with a fine hair called lanugo. This now has begun to disappear and the skin becomes brighter and is covered with a white, cheesy material called the vernix caseosa. This almost entirely disappears during the next month, but frequently there are portions of it remaining on the body at the time of birth. The fœtus is fully developed by the end of the ninth month. Then its average weight is six or seven pounds and the length twenty inches.